I used iDrive for several months but it was slow and unreliable (and did not do "continuous" backups, only scheduled backups which are less effective for a laptop. In the end, I switched to Backblaze and haven't looked back.

I started by trying the free storage option and for 2-3 consecutive days I had trouble loging in. I contacted support, we exchanged a couple of mails but nothing of what they proposed worked. The problem went away by itself afterwards. So I decided to try the 150GB for 5$/mo. plan. It took me ages to upload my data (I know its not their fault, all dsl connections are asymmetric). Then I was happy for about a couple of weeks, with automated backups keeping everything updated, until I changed the names of the folders of my photo collection. The program uploaded the folders again without deleting the older versions, and when I try to sync it gets stuck and it doesn't delete the older versions in the cloud. As a result my quota of 150GB is full and I cannot backup anything new. This has been going on for a while now, and the help desk is eager but unable to help.
I am seriously thinking about switching (that's how I got to this forum) because I cannot afford to spend so much time and energy on the issue. Any suggestions? I am considering Crashplan, SpiderOak and Backblaze in that order.

IDrive recently started offering an unlimited backup plan in addition to their free and pro plans. There are a few limites like the mapped drive support is not available for the unlimited plan, Windows only and only one computer but it is an attractive plan for those people interesting in an unlimited backup plan.

Some details can be found here: http://www.onlinebackupdeals.com/idrive/idrive-unlimited-plan-details/

Long have I been trying a software with such lots of leftovers after uninstall.