We did a split stay in summer 2010 and it was so great that we are doing another one this trip (sort of). I have to say that DH was really against doing this, but now that we have done it, we would not hesitate to do it again. Disney makes it so easy to switch resorts that it is so worth it.
There are still 2 sticky issues with this.
#1 - You have to check out of one resort by 11 and the offician check-in time at the next resort is 4. This wasn't a big deal for us, because we just checked out of one, left our luggage with Disney to move it for us, went about our business for the day (we did DTD that day) and when we went "back" to our resort after lunch and shopping, we just went to the new resort. You can do the same thing at a theme park or water park. If you make your day "about" the move, you might find it very time-consuming and thus a waste of a day of your vacation.
#2- You can't do the dining plan at both resorts unless you want to pay for base tickets at both resorts. We used TiW for the trip we did our big split stay, so no dining plan. If you purchase a package at your first resort, your dining credits are good until midnight of the day you check out of your first resort, so you can still do dinner on your move day...then you could pay for the rest of your meals OOP. If the dining plan is really important to you, you are better off staying at one resort...or making your stay at the first resort longer to take advantage of the DP longer (4/2 instead of 3/3, maybe).
We now love splitting! It is a great way to sample more resorts!