Hi,
I was trawling around and searched "marathon" and hit this thread. I have run both the 2009 and 2012 WDW marathons - both of which I can safely say were two of the best experiences of my life thus far.
The first time in 2009 - I was by myself and stayed offsite (it was on the way home to Melbourne after 6 months studying in Edinburgh, so I was too broke for an Disney hotel), whilst the second time I went back with my girlfriend and we stayed at AKL (had wanted to target OKW, but was too late booking).
In 2012, my girlfriend ran the half marathon on the Saturday and I ran the full on the Sunday. The big upside of staying onsite is using the disney transportation (buses, monorail) to get to the start / finish line. If you stay at OKW, you can even be a bit cheeky and walk across the highway to the start line.
The course itself is very gentle (i.e. it is FLAT like the rest of Florida - the biggest hills are going over a couple of highway overpasses), and both years when I ran the weather was a very comfortable temperature (thinking maybe 14 degrees celsius at the start at 6am, rising to about 20 when i finished at 9.30ish - it does get a little warmer for those finishing later. Although, it is also worth noting that in 2010 (I was in Florida but didn't run), Orlando was hit with a cold snap and the temperature was around 5 degrees at the start time).
All events are extremely well catered (I have heard people complain that it is relative expensive for a marathon entry fee - but I think it is fine, and you certainly get a really well organised event for the cost). There are drink stations every mile, medical tents every couple, and 3-4 food stations (bananas, gels, then chocolates at the last one!) as well. The pre-race pick-up and expo is well-run, the event shirts are good quality, and best of all, the medals are pretty unique.
I signed up two weeks ago for the Goofy at WDW in 2013 - so may well see you there! Let me know if you have any other/specific questions and I'll try to help...
(As an aside, in 2009 I bumped into another Aussie whilst running (I identified him by his singlet which had a decal reading "26.2 miles... No worries mate") and an Aussie family who were cheering home their daughter with Australian / boxing kangaroo flags at the finish line. The daughter had convinced her mum to bring the family to Disneyworld to run her first marathon... nice.)