I agree..CCleaner rocks for disk cleanup*, and gives you plenty of options wrt deletion and exclusion. Even before final deletion, it gives you a list of items marked for deletion. Anyway, I've never had a problem with CCleaner in all the years I've used it; on the contrary, it helps to quickly reclaim some 'wasted' disk space and clear out browser caches, menu links etc all from one convenient location.
As for defragging, things changed a bit with Vista and Windows 7 compared to XP. The included defraggers in both these OSs do not play well with the volume shadow copy service when the formatted logical cluster size (usually 4 kB) of the volume is less than 16 kB. There is a technical explanation for this, some of which goes way over my head, but the gist of it is that running the windows defragger can result in the deletion of older system restore points and creation of new shadow copies on the disk. The freeware defraggers also exhibit the same problem since they are pretty much the windows defragger in nicer clothing. The only exceptions are some of the commercial (not free) utilities that have shadow copy compatible defrag modes.
* I don't vouch for the registry cleaner component in CCleaner since I never use registry cleaners myself.