Apparently, the file %APPDATA%\Microsoft\Outlook\outcmd.dat, where customized toolbar settings are stored, can become corrupted. I think a source of such problems are add-ins such as Google Desktop, MSN Toolbar, Spambayes, antivirus with Outlook support (Avast!, AVG, among others), and so on that may have been installed and uninstalled. If you are experiencing general slow-down or weirdness with Outlook, rename outcmd.dat when Outlook isn't running and restart Outlook. Outcmd.dat will rebuild. My corrupted outcmd.dat was 12K, and my new file after reapplying my customizations was 6K.
PS I don't recommend Spambayes (anymore). Even though Outlook's built-in Junk Email protection could use some interface improvements, Spambayes really slows Outlook down.
