The correct way to re-register IIS.
Anatoly Lubarsky deserves the kudos for this information about re-registering IIS, found originally here: http://blogs.x2line.com/al/archive/2007/07/15/3203.aspx.
I have to admit that I am guilty of using the brute force method of "aspnet_regiis -i". However, the "correct" method (which after a quick trip to the docs, does seem more reasonable and less destructive) is:
aspnet_regiis -ir -enable
and then
aspnet_regiis -s path
The first is similar to the -i method, but installs only to the root web and enables the Asp.Net version that the aspnet_regiis.exe command belongs to.
The second command needs the IIS path (not file path). This should be of the nature "W3SVC/1/ROOT/AppName" where the AppName is the virtual root of your application. The full webroot name can be found with:
aspnet_regiis -lk