One small point that might be helpful for some - and I found this to be true of both Mozy and Carbonite (I am currently a Carbonite customer but asked Mozy about it): 

They keep deleted files for 30 days as a rule - and those count against your usage. I didn't think I would use much space - but I take a snapshot of a handful of website file systems and databases each day (but only keep the latest three of those) - and it turns out to have bumped me up to the next rate plan above where I expected to be.

Not a deal killer by any means for me - but a good thing to know about in advance. And as far as I can tell - functionality wise - not deleting things instantly is about the only difference between these explicit backup services and DropBox (oh yeah, and backing up multiple folders).