I'll credit Gary Marmillon of Ponchatoula, Louisiana, as the first to enlighten me (he also was very polite).
To paraphrase Gary: If you buy a Mac before the Intel switch-over, you should have little concern about software compatibility. As Apple CEO Steve Jobs himself said in his keynote speech at the Worldwide Developers Conference announcing the Apple-to-Intel move (and yes, I did watch the video), all that developers will need to do is click one box in the Xcode programming software (the primary application for Mac development), and their applications will run natively on both IBM PowerPC and Intel CPUs. You should see no performance loss on software programmed this way, and no emulation software is required.
My initial answer pointed to the Rosetta
emulation software as the crux of the matter, and that was incorrect. Rosetta, according to Apple is "designed to translate currently shipping applications that run on a PowerPC with a G3 processor and that are built for Mac OS X." That it should do with no problems. My follow-up question had to do with backward compatibility, if, for example, you wanted to run a newer Intel-based program on a PowerPC-based Mac purchased today. This is not an issue because of the aforementioned ease of making a universal binary that will run on both platforms.
So, Daniel E., and anyone else who may have seen my original answer, I hope you see this and feel no reservations about buying a new Mac. Apologies if my original answer made you feel otherwise.