Much as I love Windows Vista (yes, I know I'm slightly biased) there were a few issues that irritated me:

1. When exiting the photo screen saver there was sometimes a really long delay. This bugged me to the extent that I stopped using the photo screen saver
   
2. The "estimated time remaining " calculation seemed to take ages to appear, particularly for really large files
   
3. When resuming the machine from hibernation it would sometimes take a long time to display the logon screen.

None of these ruined my quality of life but they were painful.

But the good news is that they've all been fixed, along with a host of other issuettes, in a new service pack. Hurry along to http://support.microsoft.com/?kbid=938979 to get your copy!