Watching the time-lapse pics on Bearcam, I saw the group turn around before the ice-surface water flow.
I've never tried it but my understanding is that these things can get up alot of speed up so maybe the skimming effect helps save them. The stopping/turnaround thing these guys did may have made them vulnerable.
A quick search on google gave me this link to their sport.
http://www.iceboat.org/faqiceboat.html
I"m sure there are many more.
And yes, although I've taken many chances in my life, I'm sure I wouldn't have been out there doing that yesterday without a lifejacket or even a full exposure suit.
Three of my favorite pics from winni.com are of vehicles that went through the ice. I can't find them in the gallery to link to. I have local copies I can repost. I think they're from '03