Really not a big problem on vacancy for the cabins.
99% of the time when I'm looking for a campsite or even a Value Room and there is no availability, the cabins pop up as an alternate choice.
Also, even though you can't book online, or book a package till the 2011 rates come out, you CAN book a room only room 500 days from your departure date.
Just call 407-WDISNEY and make your reservations. You will have to pay a deposit of 1 night at the current highest rate they have. Then when packages come out for next year, you can adjust your reservation to whatever package you desire, or if you don't want a package, your rate will automatically adjust to the appropriate rate for your time period.