Recent news on FastPass: Read an article on WDWMagic.com that starting on March 7th, they are changing the fastpass rules. You will be able to enter the attraction 5 mins prior to your time and ONLY 15mins after your stated "end time". You will no longer be able to get a fastpass during the day and use it later in night after your window of time has expired. This would be a nice subject for another thread.
I too am the unofficial
Disney travel agent where I work. Over 2000 people here and I think I have talked to at least 1/2 of them about trips to WDW! Most people come to me with plans to only go for 3-4 days. Convincing people that they will be soooo rushed once they get there and figure out how big the place is and how much there is to do is so difficult and usually unsuccessful. First tip, go for at least 5 days. 1 day per park and an extra day for going back or just relaxing. Minimum. Put a loose plan together and get a couple ADRs explaining that eating at the CS will get old after one day.
One family I tried to help was determined to only go for 5 days, but was taking a day at Daytona, a day at Universal and 3 at Disney and they had 3 kids under the age of 6. They came back exhausted and feeling ripped off because they were so rushed.
If sharing accommodations with other people, make sure sleeping arrangements are fully understood BEFORE you go. DW and I took my wife's BF with us and long with a good friend of hers', so it was DW and I, wife's BF and her good friend, friend only. We paid for the 1 BR at SS, essentially giving them a free room for their stay. DW and I took the bedroom and our friends had the pullout couch. Oooh baby, this didn't go over very well.
If traveling with a large group, say like two different families, give each other some space. Separate and let them explore on their own. Meet up for meals if you must, but give everyone time by themselves.
Stop and watch some live performances. Most are less than 15 mins so you don't miss anything by stopping. This is what makes Disney so special.
Don't over pack. You'll probably bring something home. By a cheap luggage scale ($7 at %#^Mart) to save you from repacking at the resort check-in or worse, at the airport.
Do pack a power strip. You don't realize how many electronic devices you have that need charging until you only find one or two outlets in your room.
Don't rush out of the parks as soon as the fireworks are done. Everyone has the same idea, get to the busses and get out....Take your time, walk around and enjoy the lights and walk through the stores as you work your way to the front of the parks. Sit down and relax, give the crowds a chance to thin out.