Don't take it personally, they didn't respond to my thank you letter either but then ended up offering me a pre-match. Actually I don't think anybody responded to any of my thank you letters. I also thought it was a really great program, really cool people too, just too damn cold in CT for me.
from having been on the "other side" of interviewing/meeting lots of applicants... i don't think i've ever responded to a thank you note. if someone writes me and asks me specific questions i'll certainly respond, but i don't typically reply to thank you notes. i agree with ogrady. absolutely DON'T take it personally. there are plenty of applicants/candidates i've really liked but it never occurred to me to write back in response to a thank you... good luck!!