Here's my favorite hotfix:
http://support.microsoft.com/?kbid=842706
We'd use these WinForms that had usercontrols embedded within usercontrols. Sometimes, for no apparent reason, you'd open the form and ... it's blank! All your work laying out the controls, poof!
This hotfix works and isn't deadly, and was only available via our MSDN Universal right-to-beg license. It should be available everywhere.
Happy to share from my own server:
http://www.developerfood.com/hotfixes/KB842706hotfix.zip
Got some other great hidden hotfixes? Let me know and I'll host them for use of the people here.