I've posted an analysis about the recent sudden rise above 120 on MtGox here: https://bitcointalk.org/index.php?topic=278643

It might not be directly relevant to the discussion in this thread, but I think it provides very interesting insight into what is happening on MtGox now.

Short summary: The big move of mtgoxUSD on Aug 19th was a result of a very few (about 15) very large (1000-2000 BTC) orders, which were done by a handful (1-4) of individuals. For the full analysis see there!