Here is a great post about tweaking Vista and what features you might want or not want to use. It aslo defends some features in Vista that more than a few people have attacked by not understanding "why" the feature is there.
http://forums.anandtech.com/messageview.aspx?catid=34&threadid=1999401&enterthread=yHere is a brief table of contents of the post:
32bit or 64bit?
User Interface
Networking
Unnecessary Apps and Services
Windows Security Center
Audio
File System
Application Compatibility
Power Settings
Backup
Gaming/Drivers/CPU
Task Scheduling
Optimizing for low end machines
Bad tweaks