I thought Nexus 1 & S were. Dinc maybe?
You keep the stock kernel. Other than that, not much.
Oh, and the Nexus 1 and S are not made by Motorola, so...
Can't flash alternate recovery. That means its never fully guaranteed to be there. I've never personally had a problem with it but still, I'd like that type of security. Also the scope and breadth of roms is more limited since they have to be built with the Motorola firmware as a base.
tappin and a talkin