well damn, i thought i applied to alot of schools, now i'm thinking i need more! well, no, not really...too much money and time. i applied to 18 and spent a long time trying to figure out which ones to not apply to (had a potential list of 25 or so) because i'm short on cash, so i came up with dumb reasons. like, i didn't apply to creighton for the simple reason that i really don't want to live in nebraska for 4 years after being in indiana for 4 years, no matter what happens. stupid, no? now i wish i did, and i still might.
anyways, if it helps, my counselor recommended to all of us to apply to around 15, so i'd say keep it in the 15-20 range. if you apply to too many, i'm thinking schools might ask you why, they might think you are desperate and have no real desire to go to their school. but really i can't tell you for sure, i mean i'm only applying myself right now.
although that may not have been coherent, i hope it helps. good luck!