Fall is great up there, as is summer if you're climbing in the shade. Spring can be wet, cold, and bad, but there could always be good weather.
Routes there are pretty stout and the pitches are long and sustained. Some great .9s are Soler (that's the most popular .9 on the tower, a stellar two pitch thin hands in a corner), Assembly Line on the North Face, which is really steep and pretty hard for a .9, and maybe Gooseberry Jam, which is a little less traveled because it's of lesser quality (I haven't climbed that though). Also check out Bon Homme Variation and El Cracko Diablo, two great 5.8s.
Frank (bigwally on sp) graciously lets climbers camp on his lawn for free, bring a couple bucks for donations. Can't beat the location!