There are some major bugs in 10.3.5 - like the Safari cookie bug and the NFS bugs I already mentioned, and the Firewire bug mentioned by Gopher (I haven't personally encountered that one).
Also, performance of sharing in general seems to have deteriorated significantly since 10.3. We have several PowerBooks at my company, and they all used to rediscover AFP shares when woken from sleep, even when moved to a different network, connected via the AFP share via VPN. Since 10.3.2, this has not worked so well - the connection just times out. Shame - hope they can resolve it.
Also, the log in screen - when connected to a network with a Mac OS X server with Open Directory, the "Other" login option takes some time to appear. If you have already selected an account from the list and have started to type in your password, the window goes funny and it takes you back to the list again. Very annoying!
I could go on and on - Apple has plenty of work to do!