What we need: a graph showing the number of transactions to and from 2-of-3 multisig addresses plotted against time.
I'm working on this at the moment. Parsing the blockchain is taking forever.. Took an hour to get to 83000. Then a further 19 hours to get to 128500.. I'm recording txid/vout/address/blocktime for all payments to scripthash addresses (version byte \x05).
Once I have this I should get a nice plot of payments to multisig addresses, and then rescan looking for vins spent from multisig addresses. There'll probably be a good deal of lost BTC sitting at these addresses.
You can list multiple addresses and spends in the output of a transaction.
Make sure to add your own as the multisig raw transaction requires a change address.
The change address is the address an extra coins go to from the transactions.
It was not explicitly covered in the multisig section of the wiki last time I looked and I lost all my coins as a result... all my testnet coins which are still a bother to get without a gpu rig.
donations for testnet coins mfZqJvCNgJPL2y84KgamRcxUw9SUMPmej9 if you find this helpful.