SLOW STARTUP OF THE COMPUTER: Extreeeeemeeeeely sloooowwwww start-up of the computer. But you know, there is a way to fix it. Useful fix: Delete the 'Servers' folder in your 'System Folder'. Yep. That's it. Hours and hours of your life back. You're welcome :-)
SLOW STARTUP OF FILE SHARING: Extreeeeemeeeeely sloooowwwww start-up of file sharing.
RE-INSTALLS ARE FORGETFUL: Every time you have to re-install the System software, the system forgets all your settings. Pro users have learnt the drudgery of copying old Preferences Folder files, but a simple utility could do this, making sure that basic Preference Files are not copied, only applications specific ones, to reduce any corruption carrying over. Call it 'PrefsSaver.'
GENERAL: There are too many things to go into here. For more rants on the OS, have a look at www.liquid.org - Discussion Based On The Mac