I too am experiencing the same problem. I down loaded Defraggler today, and ran it.
Prior to running it I had 150Gb available, and after have 140Gb.
I have been a regular user of CCleaner, and delete system restore points on a daily basis. My first thought after running Defraggler was to delete restore point, but there was only 1 available to delete.
As a result, I feel that Defraggler has used up over 10Gb of disk space. I have not run any other applications since defragging (other than CCleaner and FireFox).
Please advise any other solutions?