I'm fairly certain the hotels for 2009 were different than 2010, so next year will probably have different resorts as well.
The prices were discounted off of regular rates, but I actually used a pin code and it ended up being cheaper than the race rate. I believe a lot of people used the buy 3/get 4 deal that came out as well. It's best to just 'shop around' and see what the best price is for you. Also, when the race discounts came out, they were whatever price, but then a few months later they went up, so book early if you plan to use the race discount.
The race discount on tickets, however, can be used whenever. In fact, friends who ran with us decided they wanted one more day in the parks, so the day after the race they ordered a park hopper ticket online via the race discount website, and picked it up at the hotel desk.
I thought it was beneficial to stay at a host hotel. There were regular coach buses that took us to the WWOS for the expo. Otherwise, you would have to catch several connecting buses to get there, and that can take awhile. Also, the transportation on race day morning was great. It was one less hassle to worry about, and free! (For the record, we had to take a cab from Epcot to Port Orleans Riverside and it cost us $13! That's only b/c we were running late for our Magical Express bus on the last day there.)
Oh, and I had said the host hotels came out last year in May but I was mistaken. I believe they were released in June.