I bought a year of CrashPlan Family service for my dad and sister. The backup service went down a couple times for DAYS and WEEKS at a time. Sounds extremely similar to this poster's experience. What the hell use is that? Eventually in their case it did start working again, but obviously going many days without backup is not really backup.
For instance: https://crashplan.zendesk.com/entries/457404
The other one I had was once when I was trying out CrashPlan for the first time. I had rsync-based backups too, and was just testing out crash plan. A hard drive failed and I tried to restore my 60-GB home directory. It took something like ELEVEN DAYS. And, it fucked up all the mod-times of all my folders. They may have fixed the mod time issue since then, though, I think.
I would never rely on CrashPlan for anything.
When I want easy-peasy backups that work perfectly, I use Arq (Mac-only). Unlike CrashPlan, it is both fast and extremely reliable.
But, that isn't an apples-to-apples comparison; since Arq (securely) backs up to Amazon S3, it costs something like a hundred times more than CrashPlan, which has flat-rate 'unlimited' storage (which is of course extremely limited by their bandwidth throttling).
I wish CrashPlan was good, but it is not. That doesn't mean cloud backup is inherently flawed, though. You would have to do a great deal of work yourself to implement backups as reliably as Arq.
http://www.haystacksoftware.com/arq/
(Not a stakeholder; just a fan.)