It's an excellent service but sadly just like Gmail is nestled snug in Patriot Act-landia.
Well, since you've breached the subject of the PA...
Which service providers can you recommend that are protected from such issues?
In all truth, if the government wants your emails, they will get them. Emails can be subpoenaed by court. You can run your own secure mail server and all, but the communication can always be intercepted by a middle man. If you have the need for a truly secure email, encrypt the message, it doesn't really matter what service you use.