I've got over 800GB with them so far and counting.
How many disaster recoveries have you successfully performed?
At least two so far; one where a major project was corrupted and I was able to recover data via their online tool (30 day rolling history.) I lost only a few hours of work in the end. In another case, I deleted a minor file in a software project and I wasn't able to recover it through the ordinary Windows processes; I would have lost a few days work so not too bad but in the end no time lost at all, other than the time required to find the file.
I normally use revision control for software but it was a project where, for silly reasons, I had decided to not use git, perhaps earlier frustration put me off it.
In lost time alone, it's probably paid for itself.
FWIW, my backups are encrypted and the key is something only I know, so I'm not worried about that aspect.