On this report:
Quantitative Analysis of the Full Bitcoin Transaction Graph
http://eprint.iacr.org/2012/584.pdfPage 11
Instawallet has 633,606 in accumulated incoming BTC
At 47.50 it is worth 30 Million Dollars!!!!
If Instawallet has fallen, this is Bitcoin's biggest theft.
But what about how many bitcoins have gone out?
EDIT: actually even if that number is right- it doesn't mean it's worth 30 millions dollars. Technically it's worth nothing as they don't make a profit (as far as I know). If they steal it all, that's another story.