Here's what I've heard...
If you go at one of the busier times of year, the parks can and will fill up and you won't be allowed in. When it gets near capacity, only guests of the Disney resorts will be let in. This would probably be during Christmas vacation, Spring Break, etc. It would suck to go all that way and then not be able to get in.
We went in early June. The parks were a bit crowded, but not exeptionally so. And the heat (for a Texan) wasn't too bad either. We were able to see most of what we wanted to. Needed 2 days for the Magic Kingdom though. BTW, it does seem so much bigger than Anaheim. As all the parks there are. But if you've got kids, the Magic Kingdom is THE place.
Disney resorts looked awesome (especially if you want to immerse yourself in everything Disney), but are very expensive. If you don't want that extra safety net of being allowed into the park when they're filling up, we stayed right off Disney property at what was probably somebody's Florida condo rented out when they weren't there. Nice accomodations and a pretty nice community pool.
We got a 5-day Disney pass and I think they were park-hoppers. We could go from one park to another the same day if we wanted to (but didn't end up doing so). We didn't do the Disney water parks. I figure why spend a day in Orlando doing something we've got at home. But there are the 4 Disney parks. Epcot, Animal Kingdom, Disney Studios, and of course, the Magic Kingdom. We had a 5 and 6 year old and managed everything but the Magic Kingdom in a day.
We also got a 7-day pass for Universal. At least at that time of year, they had a special going on. For something like $10 more than the price of a single-day ticket, we got week-long tickets. It gave us access to both the Studios and Islands of Adventure. Both very cool. It might have been one park at a time though.
Both places have, I don't know what you call them, but the ability to reserve rides. At Disney, I think it's included. At Universal it was extra, but was worth it. You basically can reserve one ride and you get a time to come back. When you do, you go to the front of the line. Do this for the rides with really long lines and while you're waiting, hit the rides with short lines.
If you want to do any special things within the parks, see if you can book them in advance. We booked for a Disney Princess luncheon at Epcot and also for the German restaurant there. Some of those special dinners are all booked in advance.
In addition to the parks, you're probably going to want to visit Downtown Disney and Universal City Walk. If you go to the Universal parks, you'll pass through City Walk on your way in and out. Lots of cool and themed restaurants and such at both places (Bubba Gump Shrimp, Emril's, Jimmy Buffet's, Hard Rock, House of Blues, NASCAR, Rainforest Cafe, etc, etc.). The absolute coolest thing to see at either was, I thought, the Lego store at Downtown Disney. Outside, they have a Lego sea serpent in the pond as well as a lot of other huge Lego statues. There's also a permanent Cirque du Soliel at Downtown Disney.
We also took a day and drove over to NASA (about an hour away). Also hit some east coast beach. We also took some time to go over to Clearwater. I love the Gulf side with it's warmer waters, white soft sand, and amazing sunsets a lot more than the Atlantic side.
