The guys who do the double IM are awesome... I rode up there to watch this years race (multi-tasking by combining a long training day with supporting another event). It's all about pacing and nutrition at that point, my club member who took part was in 3rd place after the bike but hadn't eaten enough so really suffered on the run - it was difficult to watch, however he did finish and will be back to do it better in another year.
The winner is a very focused athlete - he did it in 21hrs. Thats 2 back to back 10.5 hr IM races. Awesome.
I don't think any athlete missed the cutoff in this years race, but some did take almost the full 35 hrs to reach the finish. Anyone taking part is sensible enough to call it a day when it'd be clear a cutoff couldn't be reached (you'd know a long time beforehand by looking at average pace data) and save themselves for another day (year?).
If the double looks hard... consider this beauty:
AFAIK it has been put back another year to 2010 so you've all got plenty of time to train up for it.
Safe to say, I won't be doing either the Double or the Deca for the forseeable future. I'd never say never though.
Edit - re sponsors / prize money, it's not about the money to these guys, it can't be, otherwise they'd have gone and done something easier like fanny around on a football pitch for 90 mins each week for £1000 per minute