Hardy was so awesome, but Intrepid is buggy. Text disappears from buttons, Firefox does strange things and the sound acts funny sometimes. The focused window isn't always on top (most annoying when it's the shutdown menu) and sometimes it freezes on the password dialog coming out of sleep.
The biggest single problem for me was the lack of a real-time kernel (which I wasn't aware of until after upgrading). Since I'm an amateur multimedia producer I need it badly.
Instead of returning to Hardy I just switched to 64 Studio, but it didn't work so I installed Fedora.
In-between I had to spend the day in Vista. It's SO annoying! I guess you get used to it, though, since nobody but me seems to mind.
One parting question: How can I get the Ubuntu "Human" GNOME theme and icons in Fedora? The black, white and blue of Fedora is very ugly.