slowness is the only thing if you dont have a fast enough machine. if you have any of the G4s, you should be fine. ive heard some complaints with the G3 iBooks but not everyone. i think its a beautiful OS and its well organized too.
Im going to have to agree. I have a 600 mhz ibook that is awfully slow inside of OSX. Im guessing the lack of ram is the problem though. Right now I only have 128 MB and top claims only 5 or 6 MB of physical memory are free. I will let you guys know how performance is after memory upgrade. Speed issues aside, its an excellent OS.