As PhysicsOverflow approaches its public beta (the term beta seems still appropriate as we will start out with only the Q&A section ready first, and the full-fledged site will then include the Reviews section), it gets time to reconsider how we best promote PhysicsOverflow to the right audience. Such discussions have already been started on the blog at the beginning of last December.
Lubos Motl (who thinks our site is cool ;-) ...) gave me the advice to use some clever promotion methods, so please list corresponding ideas in the answers below.