I'll lend my voice to the chorus here... I have used Carbonite on my v10.6.8 Snow Leopard MacBook without much of a problem for more than two years until recently. (If you don't count the trip to the Genius Bar to ascertain why my fan seemed to be constantly running.) Within the past six months, Carbonite has begun to hog most of my processor at very inopportune times.
Recently, it has begun to run backups far too often (and for far too long.) I called Carbonite a few days ago and was passed to a second-level support tech, who I allowed to take control of my computer. I watched as he jumped through the depths of the various Carbonite file trees, deleting files as he went. For a day or two after that, it ran fine again. And then the problem returned.
Last night, for example, it supposedly began a backup at midnight... but five hours later it was still churning away, "backing up." Unless Casper the Friendly Ghost was downloading HD feature films all night, there couldn't have been any new files put on my hard drive that needed to be backed up.
Like many here, my only work-around has been to Pause/Unpause Carbonite, and occasionally Re-Install the application.
Could my MacBook power settings have anything to do with the problem? My settings are set to put both the computer and display to sleep after ten minutes of inactivity. Also, the box labeled "put the hard disk to sleep when possible" is checked. Is Carbonite being stopped when my machine goes to sleep, and restarting when I wake it up?
I don't think that is the issue - the backups still run too often and too long while I'm actively using the machine. But I may change the power settings just to test the theory.
If that doesn't work, I may jump ship to something else for my offsite backup. (I don't back up locally, to another hard-drive. Not since I had one go down and wipe some important photographs.)