For my work (I know, it's meant for consumers..) I've tried several as we'd like to backup everything several times.
I first tried Backblaze. It's slow (as its US based, and im EU based) and it wont backup a NAS. Tried it for a while, in the end, I dropped it.
Then I tried Mozy. Same story as above, US based, and wont backup a NAS.
I then gave up a bit, especially since they couldn't backup a NAS.
A while later I found Mozy.co.uk. Same company, different datacentre's/servers.
Servers closers to me. Thus faster uploading.
In the meanwhile, things changed at my work. We bought a server dedicated to backups. We also got a new internet connection with 10mbit up (instead of the 1mbit we had).
So we tried Mozy.co.uk. Gave us an upload speed of 7-8mbit, thus almost using the entire upload line!
We just had 1 problem/issue: how unlimited is unlimited?

(the amount of data uploaded to Mozy)
And we're not even half way. The question now is: how long will it take before they suspend us, or will they just leave us alone?
What are your experiences with online backups?