Most things should be similar. Proprietary drivers (like for graphics cards) obviously won't work (though the firmware should, I reckon, since that's independent of the host CPU). Proprietary software in general probably won't work unless you can convince the vendor to ship a POWER build. Even some FOSS might not work fully (or even at all) if it relies too much on specific architectures (in particular, I know V8 - and therefore both Chromium and Node.js - only very recently got POWER ports).

I personally run OpenBSD on all my (Apple) PowerPC hardware; it seems to work a lot more reliably than the Linux distros I've tried (in particular, I remember the install process for Debian being rather painful on PowerPC due to OpenFirmware, while OpenBSD is just as easy as it is on x86: mash the Enter key until you have a working system; at most, I sometimes need to tweak some boot settings at the OF prompt, namely if it was previously running OS X).