Currently, the parks are very quite. This year they are even quieter than normal, and this is our 4th holiday around this time of the year. However, that is partly to do with the credit crunch having a delayed reaction on Disney. Most people have their holidays booked a year or more in advance, especially those from abroad, so holidays were booked and paid for/budgeted for, before the credit crunch hit.
Almost all rides have been walk-on, except for Toy Story Mania, which the shortest queue I've seen for that so far is 50mins stand-by. Most others at our Dis Meet last night said the same - all rides have hardly any queue, except from TSM! We are hoping to do it tomorrow after DTD Check-In and before breakfast!
Normally though, it is still quiet, with waits around 15mins rather 60+mins that the summer brings. The temperature is normally a little lower than the summer period, although there have been above average temperatures the entire time we've been here!!!! There are usually afternoon showers, lasting only about an hour max, and usually around 2-5pm. The other thing to remember is that September is the height of the hurricane season, with the 10th (I think) being the most active day in the season.
Just watch out for the weekends, because no matter how quiet the parks are in the week, at the weekend they will not be! The locals and those within driving distance descend on the parks. This year, because of the extreme quiet, the weekends have been a sharp contrast to the weekdays!