I helped a friend put a pair of those new ultegra brifters on a Trek Madone. They seemed pretty cool. No funny cables coming out the sides.
It made me wonder how they might work on an older bike, with say shimano tricolor 6400 brakes and derailleurs. From what searching I did it seems like shimano is saying that the brakes are not fully compatiable. Like they use different pull rates or something.
I didn't find anything with regard to the front or rear derailleurs. My best guess is that the RD might be ok, but I have no idea on the FD.