I upgraded to Office 2010 yesterday. So far I have only used Word and Outlook but been very pleased. I did have an issue reconnecting one of my pop accounts and was getting a unable to access data file. I deleted the account and added it back to correct the issue.
I also cleaned out my Saved folder and started to use the categorize features to sort email and tasks with good results.
I also upgraded Visio and Project but have not used them yet.
So far I like the new interface and the performance is really good.