A problem that's been in my head since Apple announced their transition plan to move from PowerPC to Intel processors is one of fairly serious concern - professional applications. While I imagine that many of the smaller Macintosh developers or long time Cocoa (Yellowbox/OpenStep/NeXTStep) will have applications ready to go when the transition occurs, it's a different story for professional applications.
Andreas Pfeiffer picks up on this in eWeek. He covers many of the issues that have been troubling me, and he seems equally troubled about them. The overall message is still a bit uncertain right now - what about 64 bit? What about AltiVec? These were considered chief advantages of the G5 over an x86 based architecture and were rightly touted as such over the last couple of years for developers to take advantage of. On the lower end of the scale, there are few things to worry about here. Lower end audio applications, for example, written expressly for Mac OS X probably use Apple's standard libraries and subsystems such as Core Audio for plug-ins and other audio processing, and aren't likely to be affected. But professional applications like Pro Tools are likely to have a lot more work ahead of them. Many of these professional applications, such as Pro Tools, QuarkXPress, and much of Adobe's suite, all took their time in coming to Mac OS X. These applications have longer release cycles and cost hundreds or thousands of dollars and they're expected to work right, just out of the box. Furthermore, they depend on plug-ins. The plug-in business for Pro Tools alone is a sizable industry. Even if the next version of Pro Tools shows up shortly after Apple's professional machines switch over to Intel processors, it can take much longer for all of the plug-in developers to come on board. A few studios that I know of have not been able to make the move to Mac OS X because they still have unsupported plug-ins or may not be able to authenticate them (license enforcement in the pro audio field is legendarily rigid).
According to some early reports I remember reading about Apple's switch to Intel, Apple plans to move their consumer machines to the new architecture first. According to Apple's industrial designs and professed reasons for choosing Intel (better performance per Watt), this makes sense. Getting the G5 processor into anything smaller than an iMac G5 - a beautiful piece of engineering, but definitely too hot and too big to put on a lap yet - is apparently proving difficult, and the G4 processor is rapidly falling behind on performance. Higher end machines can probably still enjoy the benefits of power of the G5 processor and architecture and stay fairly speed competitive for a bit longer without having to worry about fitting into smaller spaces and the associated cooling challenges. In the meantime, Apple's laptop line can also catch up on performance without the apparent G5 heat / space issues over the next couple of years.
Apple's current long-term plans are pretty vague. I know there are quite a few Mac purchasers - whether individuals or corporations - that are worried about making purchases now on what seems to be a dead architecture. There are at least two years worth of new PowerPC based products yet to come from Apple, and I imagine that they're all going to remain adequately competitive. Beyond that, there are a couple of years at least of continued support for those machines from software.
The concept of universal binaries is that applications will run fine on both processor platforms. Developers do have plenty of time to make the crossover. I highly doubt that there are going to be any applications for the first few years of Intel based Macs that will only run well on the Intel based boxes. So a PowerPC based purchase in the near future is not going to be worthless or useless over night. Personally, I'd rather have a late model PowerPC based Mac than an early model Intel one.