Take this with a grain of salt because I only speak for myself, but I'm planning on going to all of mine (13). I think it will be rough, but I'm really interested in all of the sites and I think that I'll have a much better idea of which is the perfect fit when I interview (out of the only 3 interviews I have done so far, my initial rankings have already changed). Expensive and time-consuming, certainly, but I think it is worth it. Of course, if sites were truly back-ups and you aren't that interested in them, I think it is fine to turn them down. After 11 interviews, the match rate is at 99% anyhow. And, most folks match to one of their top 3! I just need a feel for the places before I know which truly are my top 3.