I only applied to one school (clinical psych PhD), but I had good reasons, I think. I interned all summer with my POI, I know I love the research focus, the school is awesome, the area where the school is located is wonderful, and it's my number one choice, hands down.
Also, with a fall 09 having to take the GRE, take two courses, start an honors thesis, and work full time, I knew that I wouldn't have the time or the energy to do a full-on grad app season.
If I don't get in, I am moving to the area where the school is anyways because I love it so much. So, either way, I win.
Of course, I will be much happier if I do get in. Of course.
Good luck, fellow one-schoolers!