DH and I had a bit more discussion about the US trip last night. He is really keen to spend as much time in NY as poss, he confessed to loving it so much more when we were there last year than he ever could've imagined. He said he will gladly go back there anytime so long as we can afford it so I may be able to swing a few more trips

.
So am thinking something like this for December 2011:-
11 days staying at WDW - one of these days to Kennedy Space Centre and one to Wiz World of Harry Potter which leaves 9 park days, if the weather permits we would like to have one morning at Blizzard Beach.
7 days in NY
3 days Washington
That's a total of 21 days not including travel days.
We would like to do the Canada thing as well but I feel like maybe we'll consider skipping it this time. I definitely want to go in December for this trip, I want to see the decorations because I am a crazy Christmas nut. So now that DH has said he would willing return to the US, I think we could take advantage another time of Sept/Oct dates, milder weather and we could take advantage of one of the wonderful bus tours that run from NY up to Canada and back. We may even be able to take advantage of free dining if we went at the time of year. The saving there could be the thing that makes a 3rd trip a possibility LOL.
We did discuss hiring a car last night but I am still a little nervous about driving in such cold unpredictable weather in December from NY to Canada.
Will think about that part more.