Sending to a P2SH address is standard. Spending from that P2SH address is only standard if the script that hashes to that address is standard.

The address prefix is selected to start with a 3 on the real network, and a 2 on the test network.

I don't know about Bitstamp or Mt. Gox specifically, but any service built on a current bitcoind should support it just fine. I suspect that most services support it and may not even realize it.