The time between now and approx. June 2011 will be an interesting time to visit DCA. As skiingfast said, this is probably the time where the number of construction walls is at its peak.
While there are still awesome rides like ToT, Soarin, Screamin, and Toy Story, is it possible to postpone the trip until summer of 2011? I think that would be ideal because the Little Mermaid ride will be open, as well as Goofy's Sky School and the new Paradise Garden eating area. It's not so much about the things that will be "closed" but more about the amount of things that will be "about to open", if that makes any sense.