• Applications compiled for PowerPC (except Classic applications) can be run via Rosetta.
• Native applications (compiled for Intel) run natively.
• "Universal Binary" applications contain both PowerPC and Intel code and can be run either natively or via Rosetta.

Java applications and applets as well as Dashboard widgets run unmodified on both Intel and PowerPC platforms.

An Overview:

Software	Mac OS X PowerPC	Mac OS X Intel
Carbon applications	Mach-O Carbon applications compiled for PowerPC PEF Carbon applications compiled for PowerPC Some PEF applications can be forced to run in Classic PowerPC code in Universal Binaries	Mach-O Carbon applications compiled for Intel Intel code in Universal Binaries PowerPC code in Universal Binaries can be forced to run in Rosetta Mach-O Carbon applications compiled for PowerPC in Rosetta PEF Carbon applications compiled for PowerPC in Rosetta
Classic applications	PEF Classic applications compiled for PowerPC PEF and other Classic applications compiled for 68k	Mac OS X Intel does not support Classic applications.
Cocoa applications	Cocoa applications compiled for PowerPC PowerPC code in Universal Binaries	Cocoa applications compiled for Intel Intel code in Universal Binaries PowerPC code in Universal Binaries can be forced to run in Rosetta Cocoa applications compiled for PowerPC in Rosetta
Darwin applications	Unix applications compiled for Darwin/PowerPC PowerPC code in Universal Binaries	Unix applications compiled for Darwin/Intel Intel code in Universal Binaries PowerPC code in Universal Binaries can be forced to run in Rosetta Unix applications compiled for Darwin/PowerPC in Rosetta
Dashboard widgets	Dashboard widgets are not applications in the classical sense and run unmodified on both platforms.
Java applications	Standard Java applications run unmodified Some Java applications use PowerPC code to start Some Java applications require Classic to work	Standard Java applications run unmodified Some Java applications will use Intel code to start Some Java applications use Power code to start and might work with Rosetta
Other applications	Microsoft Virtual PC allows the running of operating systems for Intel-based computers on the Macintosh desktop. Windows applications are supported and run in emulation.	Microsoft Virtual PC will likely be available for Mac OS X Intel soon enough and run Windows applications at near-native speeds. Wine (an implementation of the Windows API on Unix compatible systems) is expected to be available for Mac OS X Intel as well. Note that Wine is no emulator. See also the Crossover Office Web site.

From this application support matrix we can see that Mac OS X PowerPC generally supports PowerPC and 68k applications natively and via built-in emulation while Mac OS X Intel generally supports Intel and PowerPC applications natively and via built-in emulation respectively. Rosetta does not support code optimized for Altivec (G4 and G5 vector processing) or 64 bit code (G5). If your application makes use of these features it will not run on Intel machines unless they also support G3 computers.

Classic applications generally have a different look and feel than native Mac OS X applications but run at native speed. PowerPC applications running in Rosetta have a native look and feel but run at a slower speed than native applications.

Application support has to be taken into account when considering the purchase of a new Apple computer.

Another consideration is the advantages and disadvantages of the processor architecture. Modern Intel processors require less power and are thus better suited for mobile devices such as laptops. The PowerPC 970 (G5) on the other hand is faster (when Altivec code is employed). So depending on what applications you use and where, the decision for either platform can be advantageous or not.

Depending on what types of applications you use the switch to Intel might be more or less difficult:

Application type	Considerations	What to do
Apple bundled applications	Apple have built these applications for PowerPC and Intel for the last five years.	Mac OS X Intel will come with the usual bundled applications. Thus do nothing.
Other Apple applications	Apple have complete control over these applications and most of them should already be running on Intel computers.	Apple will definitely sell Intel versions of their applications. Free updates might be available.
Word processors, editors, spreadsheets, and other productivity applications	Productivity applications tend not to be very processor-intensive and should run well on Rosetta.	Use the PowerPC versions of the software and update to Intel or universal versions whenever convenient.
Productivity applications (Classic)	Classic applications do not run on Intel processors.	Upgrade to Carbonized versions of the software or keep a PowerPC Mac around.
Original Macintosh games	Macintosh games might be hard to port.	These games will probably not run well on Rosetta.
Ported Macintosh games	These games tend to be portable.	Updates to Intel versions might be available for free.
Macintosh games (Classic)	Classic applications do not run on Intel processors.	Update to Carbonized versions of the games or keep a PowerPC Mac around.
Multimedia applications	Multimedia applications (like video players) tend to be very portable and are usually ported to Mac OS from Linux or Windows.	Download Intel versions of the software which should be available very soon.
Darwin and open source applications	Open source applications are usually very portable. They are often installed as source code and compiled on the target system or available as binary packages for the specific platform.	Install open source software like you would on any Linux/Unix/Macintosh computer.
Unix applications with Carbon or Cocoa interface	Non-free Unix applications are usually easily ported and only require work on the user interface.	Expect Intel versions soon, possibly as free updates.

In short: buy an Intel Mac if you use only newer applications, stay with PowerPC if you use older applications. If you use mainly open source applications (and for you Mac OS X is really just an alternative to Linux), go with whatever platform you find useful architecture-wise.

Applications released in the future will of course support Intel-based Macs, and probably PowerPC-based Macs as well for a long time. However, several game developers have already voiced their happiness over how much easier it will be to port Windows games to Mac OS X if the underlying processor architecture is the same.  Games are thus likely to support Intel better than PowerPC and might not be released for PowerPC Macs at all. This is not as bad as it seems. It only means that the designated game machine can now be a Mac too.

Consider the following table.

Application type	Considerations	Likely outcome
Apple bundled applications	Apple control these applications.	Bundled applications will be on par on both PowerPC and Intel.
Other Apple applications	Apple control these applications.	Depending on how the PowerPC and Intel architectures develop such applications might be released for Intel only or for both PowerPC and Intel.
Productivity applications	Productivity applications are rarely CPU-specific.	As long as developers will have PowerPC machines, productivity applications will be released for both PowerPC and Intel.
Original Macintosh games	Macintosh games are usually not CPU-specific (if Carbon).	These games will be available for both PowerPC and Intel.
Ported Macintosh games	These games are usually Windows ports.	Intel only.
Windows games	Such are games that run under Wine but have not been ported at all.	Intel only.
Multimedia applications	Multimedia applications are released very much according to very current demand.	Very new proprietary technologies will be Intel only. Most multimedia software will be cross-platform with versions for PowerPC and Intel.
Darwin and open source applications	These applications are very portable.	Open source very much ignores the underlying architecture. PowerPC and Intel.
Unix applications with Carbon or Cocoa interface	These applications are very portable.	PowerPC and Intel for some time. Depending on development maybe Intel only in a few years.

This table should give you an idea about future application development. I believe it is most likely that PowerPC-based computers will lose games first. For all other application genres, the architecture should not make much difference.

So choose wisely. My plan is to buy an Intel-based laptop in one year and a PowerPC-based desktop in two years (2007).