I fixed my first Vista problem last week. My boss brought in his Vista RC1 machine and it was acting oddly. Explorer.exe would take 50% CPU usage (two core CPU) and the Start Menu's pin list wouldn't show up at all. Everything else was working properly (including the All Programs list, and other functions of the Start Menu).

I had to find out whether the pin list problem was the cause or the effect, so I began searching the internet for the location of the pin list. It's nearly impossible to find this information.

After a half hour of digging around with Sysinternals Filemon and Regmon, I wasn't getting anywhere. I used Sysinternals strings.exe on shell32.dll (which I had previously discovered is where the pin list calls & code are stored) and finally found out where the pin list is stored: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\StartPage
The value Favorites contains the pin list itself. I found that on this Vista machine, there was nothing wrong with the Favorites value. It was the ProgramsCache value that had become corrupted. After deleting the key and restarting Explorer, the pin list came back up and all of the CPU usage went away. Problem solved. (This all works the same in Windows XP.)