This article from coindesk may answer some of your questions although it is almost a year old now http://www.coindesk.com/year-multisig-so-far/

There's no information attached in multisig transactions to tell us what it is being used for so you can only guess. There are not any exchanges that uses multisig for any customer facing applications. There are however many online wallets, such as the one offered by Coinbase or Greenaddress , that uses multisig for better security.