I don't normally let Beta versions of things any where near my development machine because I just hate it when things become unstable. The IE Developer Toolbar, however, looks like it is going to be so useful that I just can't wait for the RTM version.
http://www.microsoft.com/downloads/details.aspx?FamilyID=e59c3964-672d-4511-bb3e-2d5e1db91038&displaylang=en