I've considering getting a Powerbook but running Linux on it.

Don't bother. OS X should cover all your Unix needs with the addition of an X Server. And they work so well, I have one loaded that gives me seamless integration, including the "Genie" effect of minimizing a Unix X app to the Dock. Running Linux on a Mac now is about as silly as running Linux on a Sparc machine. It can be done, but there is a better Unix built for the CPU sitting in the box.

To be honest, if you want the best hardware compatability and want to be able to run the latest games/software then you're going to have to run Windows on a PC

Games yes, software, no. While Windows has a ton of software, many of the programs do the exact same thing. I still haven't been able to run into an issue of specificially needing a Windows program in my quest to switch to OS X for all my non gaming PC use.

Gaming is getting better on the Mac though, so in a few years, I bet the majority of the games will exist on both platforms. Most hit games are eventually ported, but more and more are hitting the shelves ready for either platform.