I've used CCleaner since this past May and I think it's very good. I use it all the time to get my system in check. Yesterday, I decided to download and try Defraggler. I ran it on my Windows XP desktop. It installed ok and did a defrag with no problems at first. Next, I installed it on my laptop Vista. But had a problem with it there. After the install I did a defrag started about noon. By 8:30 pm it was still running and never got past 65% complete. I finally closed it. THen I discovered my web pages opened very slow. When I clicked on the "favorites" link in the top of my page, all my favorite sites that I had saved (close to 100) were no wheres to be found. I ended up doing a restore to a earlier time before I installed the defraggler. THat ended up putting all my favorites back in and my web pages were quicker to open. I then decided and removed the Defraggler off my desktop. I have great luck with CCleaner and using them on both computers, but the Defraggler caused me problems.