There are splits at both the federal and state level. I don't know where Maryland stands.
I know SCOTUS refused to hear a case recently, but I think they refused for administrative reasons. The case was not ripe yet. Also see U.S. Supreme Court nixes appeal over forced password disclosure.
Yeah, that's an interesting discussion. I don't have a good survey of email or cloud providers and how they handle keys.
At least two cases come to mind, however... Hushmail and Lavabit. In those cases, the US government just intercepted the traffic on the way to the provider before it was encrypted under the end-user's public keys.
Hushmail was based in Canada. Hushmail backdoor'd their product at the request of the US government - no order or warrant was required. Lavabit refused an order to hand over the webserver's keys. Instead Lavabit shut down the service and killed the canary.
