Looking at
http://bitcoin.clarkmoody.com/widget/chart/ it appears (based on the red volume spikes) another huge sell off and Mt. Gox pulls the plug twice in a row. I believe they do not want to see BTC under $100 and think they can control it.
I was wondering this too.
This happened the last time it went down too (12+ hours ago). I was watching orders on TradeHill's feed (and others). There were two massive sell orders @ 30 cents.