It will be very crowded. You can check out the Trip Report board for some 1st hand reports from this year. We went in 04 and it was packed. However back then I wasn't this Disney nut so I didn't have good park touring tips. Whenever traveling during a busy time the 3 top hints for efficient park touring are:
1) Arrive early early early! The first couple hours is the best time to hit some of the slow loading rides (Peter Pan, Dumbo, Matterhorn, etc.). You can get more done in the first 3 hours the park is open than you can the rest of the day. Plus you can stock up on FPs
2) FastPass! If you're not familiar with it, read Hydroguy's tips in his sticky. And if you are familiar with FP, read Hydroguy's tips in his sticky. Getting as many FPs as possible in the morning can really help you ride some popular attractions in the middle/evening of the day when their stand-by lines are long.
3) Understand each attraction. Do some research and find out what rides are best ridden in the morning, the afternoon, or the evening. You don't want to spend precious morning touring hours on rides like Pirates or Winnie-the-Pooh because their lines never grow too long even in the busier afternoon. On the other hand you don't want to wait in an hour long line for Peter Pan at 1PM. Also understanding which ride's FPs are better used and which ones you shouldn't waste your time with is a good thing to know.