From what I am reading here, Bitcoinica is running 2/3 of the volume on mtgox. I don't know how often this happens, this is the first time I made the connection, but presumably it is like this every day? I am clearly in the wrong business, as are the X number of alternative exchanges.
as of right now, bitcoinica reads: ฿40,893.38 (44% hedged)
so 17992 btc activity on mtgox was due to Bitcoinica
which was 17992/65433 = 27% of MtGox
No, it's not like that every day. What I've noticed is that there's a lot more bitcoinica activity as a % of MtGox during sideways days. And when there's a starfish all day (like on a bull market day), bitcoinica activity goes way down.