Ever since upgrading to Vista and Office 2007, I've had a really annoying problem with Outlook 2007. After running for a couple days, the UI would lose the ability to repaint itself correctly. It would glitch out and start drawing large blank regions or garbage. It smacked of a resource leak, but caused by what? I tried everything I could think of - upgrading the video drivers, disabling add-ins...nothing fixed the problem.
Finally one day I clued into something - I've been running the Outlook Appointments Sidebar Gadget for almost as long as I've been running Outlook 2007, but hadn't thought to try disabling it. Once I did, bingo, no more problems. My sources at Microsoft (actually, my sources sources) confirmed that this is actually a bug in Vista that's being triggered by the gadget. Apparently the gadget's author is working to mitigate the problem.
BTW, while trying to track down the problem I was monitoring Outlook's handle usage. Am I the only one who thinks Outlook using 2600 handles at startup (and >3200 after running for a while) seems a little excessive?