The worst is its network discovery mode, which for the life of it, can't find a machine with XP on it. Every time my sister restarts her XP machine, she disappears from the network, even though she can still access the net through my wifi. It is especially infuriating when trying to LAN party.
That's not a Vista issue. That's a Microsoft p2p networking issue. It's been a problem forever. It has something to do with computers fighting over who is the master browser.
What you should do is have one PC that is always on have the computer browser service enabled, and stop and disable it on all the other PCs. Despite the name, what this does is prevent PCs from trying to become the master browser. Instead, they always look to another master browser, which will be the PC with the computer browser service enabled. Truly, this is the solution.
As far as Vista's issues my biggest complaints are no longer really bugs, but annoyances. File transfers (not Internet downloads, but in-the-LAN file transfers) are much, much slower under Vista. It was worse before SP1 but it's still not as fast as XP, which is interesting because supposedly XP has a pretty shitty network stack and Vista was supposed to rectify that. Also, Vista is just slower. I have a brand new work laptop that has Vista Enterprise x64 and the thing just crawls. I hate the new Start menu too. The little search bar is nice, I like that... but I hate how the programs section is just a clusterfuck now. It wasn't much better on Win95-XP, but it was better than what Vista has.