I was at the caltech visit this weekend. They told us something like 30 students were invited to visit; 20 this weekend, 10 more 2 weeks from now.
The school is small-1200 grads and 900 undergrads. So the campus pretty much looked deserted. I go to school at UIUC, so seeing a deserted campus was a little depressing.
The faculty research was very science oriented. They even emphasized the fact that this was a Materials Science program, not a Materials Science and Engineering program. Faculty meetings were mostly 1 on 1, except for Professor Atwaters (PV guy in applied physics and material science). All the students say they were meeting him in groups of 3. I guess I was lucky, and I got to meet with him 1 on 1, and for a pretty long time too (almost an hour).
In my opinion, Caltech will only appeal to a very narrow group students....
Anyway, they will probably give out offers in 2 weeks or so.