- long start-up time of media player in general
- things in the background (like copying a large file) bring the OS to a halt, consequently ruining the 'multimedia' experience
- codec hassles (there never seems to be the right codec on the machine you happen to use)

maybe the thing I really *hate* most is that simple tasks such as mentioned above (copying a large file) really mess with the foreground processes. Just try to copy 100GB to a network share and try to continue to work. Or open up VS.NET and a project from VSS and then try to use media player or even open windows explorer to look for a file...