i used my gf's powerbook G4 1.33G for 3 weeks. i feel mac os is more stable than windowsXP. there are certain software only available on mac, for example, final cut.

from the spec, the new mac mini is similier to powerbook G4. i think the speed is quite acceptable, although not super fast when encoding video or mp3.

for office files. if you have office for mac, there is no problem at all.

i think the biggest advantage of apple is that it offer the complete package, both software and hardware. when something goes wrong, you can bring it back to apple store and they will be able to take care of it. on PC world, you need to deal with several different companies to solve a problem.