I email him often enough that I sometimes worry I annoy him (not that often, once or twice a month or so. always interesting to pick his brain on whatever topic and despite my worries, knowing him I doubt he minds)
I once emailed Douglas Hofstadter with some of my own ideas after reading his book (GEB) and he actually responded with a long reply.
I did write to him some weeks ago after reading GEB! Didn't get a reply, but also, I don't expect to. I just hope he reads the praise :)