The standard hardware maxims still hold true even with Apple equipment. The best way to see a performance increase is usually to increase the amount of RAM available. If you aren't maxed out, I would do that before buying a new machine. RAM is relatively inexpensive and hopefully the performance increase will give you enough time to further evaluate things when Apple decides to release some more detailed information - like, for example, exactly WHICH Intel processor(s) will be used.

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Every rule has an exception. Especially this one.

Personally I think you'll run into more compatibility problems if you buy one of the first Intel Macs (which will likely be laptops anyway).

The way I see it is, it will take some time for apps to be recompiled, and for developers working outside of XCode or on highly optimized apps, the wait could be even longer. The PPC stuff works now and I imagine everything new will work on on PPC AT LEAST until Apple ships the last G5, which I see being at least 2.5 years from now. After that new versions will likely continue to work on PPC for most software for several more years (if the promises of XCode fat binaries hold true).

I'm actually planning on buying one of the last G5s (just ordered a new PowerBook G4 yesterday) because I think it's such an amazing architecture that I want to own one while I still can. Down the road in the distant future when it's no longer supported at all by Apple's OS, I can see myself putting Linux on it to get even more mileage. Then 50 years from now my kids will inherit it and sell it on e-bay for $50,000 (not adjusted for inflation).

Of course, I could be totally wrong... but when have computers ever lasted forever anyway?