My dad (a former imagineer) explained the bug room effect to me today. It is much more complicated than one might think, which is why almost no one would know how it was done (because it seems like the effect would be really simple).
Basically, it's not a projector on a turntable as one would assume. The projector is actually completely stationary and there are three mirrors (at different angles) which reflect the image and then slide out of the way (one mirror at a time). And the image appears to slide across the round wall.
I made an diagram (top view):
(The mirror closest to the projector slides away first)
The reason the image seems to "slide" across the wall is because it is really hard to distinguish where the image is hitting two different mirrors at the same time (you'd have to examine the bugs very closely to see the break between the two angles of reflection[thus two different images]).
I think the reason they couldn't just use a projector on a turntable was due to the focal length, but I'm not certain on that.
Anywho, thought you'd all like to know that, as we're all itching for more and more info about Disneyland.