E-vaulting for backups

I have a customer who’s asking me about on-line remote backups – they’ve gotten emails and some literature from a company called “Amerivault” that is offering on-line backups and retrieval of backed up files. I have a lot of questions about this kind of service – security, access, etc. etc. Does anyone have any experience with this kind of backup service, thoughts, ideas? Anyone know anything about this particular company (located in Waltham, MA)? Thanks for any input.