I've found that occasionally we're seeing VS startup times being very slow. In one recent case, it was the MRU files/folders (that list that shows when the File / Recent Files or File / Recent Projects has references to the files or folders that are no longer reachable (say on a disconnected network drive). All you have to do is delete the HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\8.0\FileMRUList or HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\8.0\ProjectMRUList registry keys.
Another couple of hints come from Tim Noonan
If you have start-up speed issues when the Team Foundation Server is not accessible, you can add a DWORD value called AutoLoadServer under HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\8.0\TeamFoundatio and set the value to 0. That way VS won't try to connect to the TFS machine on startup. You can always set the value to 1 to enable auto-reconnect. I've personally used this trick while doing the maintenance on my TFS server.
The final trick is best described by the hippie coder himself as I've never used it
[Via Rants of a hippie coder]
Don't Automatically Get Missing Files
The next setting is to control whether or not we attempt to automatically get files from the Team Foundation Server that are missing from a solution or project. This can be very helpful when you have files that are part of a project or solution but are generated by the build process as well as situations where you are working offline.
Add a DWORD value called DisableGetMissingFiles under HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\8.0\TeamFoundation\SourceControl or HKEY_LOCAL_MACHINE\Software\Microsoft\VisualStudio\8.0\TeamFoundation\SourceControl. Any value other than zero will disable getting files from the server automatically.