Here's a couple of things we learned we visited Sept 11 - Sept 25.
The lines for the rides were very small, never really needing a fast pass.
Unfortunately this is a god time for Disney to perform their refurbs - Small World was closed, Tigger and Pooh, and Peter Pan and much of the Main Street were under refurb so pictures weren't as nice, but they do place decorative tarps up that look like the building so it didn't suffer too much. (leave it to Disney)
They are creating some new areas behind the Castle such as Belle's Story time, Beast's diner, and a castle for Aerial which may be done by 2011.
The love bugs were in full swarm which made some of the hot days a bit more irritating (especially Animal Kingdom).
During the last week in September, they are installing the Christmas Lights on Cinderella's castle, so early pictures you may wish to take of the castle will have a large boom of a crane in them, this also stops the pyrotechnics during the castle shows during the day. The crane is usally gone by evening.
Some more general tips we discovered:
During the Festival of the Lion King at Camp Minnie Mickey, the characters meeting circle was empty so my kids got a lot of personal time with the characters, Goofy actually left his pavillion to come play with them.
There are gold coins left in Cinderella's fountain (MK) if your early enough, the first batch is gold, then later silver, then finally purple. They are plastic but my kids loved getting them.
During heavy rain days, the fireworks still occur, just later (MK) and the parades reduce down to just the floats (in which Cinderella and the float riders have clear umbrellas).
Fireworks from behind castle were not as good as everyone says. There is too much too much looking forward and back because some fireworks fire from the castle and some from the rear of the park. (NOTE: during the finale, my family and I were on the Dumbo ride and it was quite a unique feeling as all the fireworks shot off when your flying high in Dumbo.)
The Contemporary observation deck on 4th floor is nice to see fireworks from, but this time there was no music.
Sitting on sidewalk on Main Street across from Bakery is great for bathroom runs through stores while parades are going on.
Strollers/wheelchairs are easier on Ferry than Monorail, sometime the cast members let you board first, get a seat. For those without strollers/wheel chairs, the upperdeck is your friend! More seats and a GREAT breeze!
will post more as we think of them.
I think I am at about 170ish on the first set! Wow, so much info! 
Thanks again! 
For a fee of $485 (yes, that's what I said!) while you are out enjoying the parks, some magic can be sent to your room in the form of, among other stuff, a sash on the door, wand, rose petals, certificate, and of course the crowning Tiara! There are three different age appropriate packages, each differing slightly. 
Or should I be concerned??? 
