I've had limited success with my backyard bat house and growing success with my two bat houses on a nearby wildlife refuge (see this thread:
bat-house-with-slate-exterior-t479.html).
I am located in the Pacific Northwest, and bat roosting behavior seems to be a bit different than in other parts of the country. e.g. the colonies seem to be smaller and more dispersed.
This summer I'll be leading a few "bat walks" on the refuge this summer, with my bat detector. We did our first one last summer and it was very popular.
I've posted lots of photos to the thread above, take a look.
Dave