James (don't mention his name in cycling circles) Cracknell did it the other year. I watched the programme they made about his attempt. IIRC he did finish, but his feet were FUBAR by the end of it.
They had to butcher his feet just so he could keep going, and at one point he was collapsing through exhaustion, dehydration, stupidity etc and was very nearly pulled out for his own sake, not to mention his Wife and kids
If your single, healthy and a sadist, go for it. Otherwise consider your family and take your name off the list and do IMUK or run the VLM instead or something.