I just did a search and found this short article:
http://www.timesonline.co.uk/tol/new...cle2056508.ece
I think that the ice constricting the blood vessels and flushing out the lactic acid is:
a) unlikely
b) not very significant if it does happen
c) a pretty cool sounding idea
d) unproven
Like pity said, contrast showers make more sense.