I accidentally keep clicking on the Send Feedback link that appears next to the minimise button on Windows 7 Beta. It actually appeared in the Windows Vista beta, as well.

Anyway, to get rid of it, you need to change a registry value:

Key: HKEY_CURRENT_USERControl PanelDesktop
Name: FeedbackToolEnabled
Type: DWORD
Value: 0

Thanks to http://www.mydigitallife.info/2008/12/08/hack-to-remove-and-disable-send-feedback-tool-in-windows-7-beta/ for that tip.