Tonight I was working on something and deauthorized my DHCP server in Active Directory (long and not very interesting story - I promise I wasn't randomly clicking things..... ).
So I just went in to reauthorize it, and I get a very helpful (ahem) message that tells me that "The specified servers are already present in the Directory Service".
Yay Google, turns out that there's a very cool part of Active Directory Sites and Service that I'd never even seen before!
From a DC, open up Active Directory Sites and Services. Normally this is where you do all of the fancy site replication stuff if you have multiple AD sites, but if you highlight the root of the structure, choose the "View" menu, and select "Show Services Node", there's a lot more to see.
Most of this stuff I wouldn't touch without explicit instructions, of course, but still neat. You can see Exchange stuff, and your certificate info under the Public Key Services folder.
What I needed to do was to delete my server's entry under the NetServices folder, and then I was able to again authorize my DHCP server.