Heh, I saw Danishefsky talk about this very chemistry last year! It was done by a post-doc in his lab who used to be a grad student at my school. Another grad student who recently graduated from my lab is now working on some chemistry closely related to this particular reaction, also as a post-doc in the Danishefsky lab.
As for the mechanism, although I don't think it is completely understood, this is almost certainly a radical reaction at some level. It is known that triethylborane can serve as a radical initiator, usually after exposure to a small amount of oxygen. The initiator probably then reacts with the iodine to generate a radical alpha to the carbonyl group which can then pick up another electron at generate a boron enolate. This enolate subsequently adds in to the aldehyde.
Here is a link to the paper:
http://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/ja0574567