I use dropbox constantly. Incredibly useful for work, but unfortunately, I can't put confidential info on there...pain in the....I'll checkout GDrive and SkyDrive....I don't trust any of them with my data though - too vulnerable to supena. I'm waiting for the first service that is both easy to use and HIPPA compliant...
The problem is there is nothing to be HIPPA Compliant with. HIPPA does not contain any kind of regulations that apply to or cover backup applications, online storage, or disaster recovery. So it is impossible for any service or application to get HIPPA certified, ergo it is impossible to have one of these services that is void of the duty to comply with a subpoena.
You also have to watch because some services claim to be "Compliant with HIPPA Policy". All this means is that they comply within their facility with the regulations in place for physical medical records. IE locked areas, security systems, data encryption, etc. So yea they take steps similar to that of Hospital Records Department's but in no way are they considered HIPPA Compliant or treated under the HIPPA act. It's like being an automotive painter in a garage and saying "I follow licensing regulations" and being a pro who says "I am a licensed painter".