I've been using it for about two years. Generally I like it. I've had a few problems, but contacted support via email, got a response it a day or two that fixed the problem. For the most part it just sits on my task bar and does its job. If there is an issue it pops up an alert.
It has already saved me big-time. When upgrading to Windows 7 I encountered a problem that wiped out my hard-drive - I was able to recover everything via Carbonite - it took a few days to get everything downloaded - but I got all my music, photos, documents etc. back. So it has been worth every penny.