I currently have 11 unused dragon souls. I've played about 90 hours total, and I have 19 shouts, and 14 of them have all three words, so... around 59 dragons killed so far. I don't particularly care for the dragons who don't seem to want to land, because I have two swords, not two bows.
Also, I was attacked randomly three times at the college when almost all of the magi were outside. the first time was on the wall, and I didn't know a dragon was even nearby until Lydia started running after it, the second it just dropped in, almost right on top of me, and the third decided that flying around getting shot at for a while was a good idea before landing.