CCleaner works and IS still free
I still use CCleaner and give updates every month sometimes even more often, it works pretty well and does a very light cleaning job. In fact I clean it every day of registry irregularities and I have never had a problem. It also asks you if you wanna save every time too and all you have to do is back it up, and if something goes wrong just double click it and the registry will go back to normal from that time it was saved.
I am aware of certain ones however that are known to cause damage, CCleaner does a very light cleaning job, and that's certainly better than nothing. I haven't had any weird problems with my computer going wacko yet nor did I have to reformat (knock on wood). It also cleans a number of other things too and wipes deleted space from your hard drive.
I would definitely say that everyone should have CCleaner because of this, otherwise you may have to face reformatting and that's really a pain in the butt I think everyone would like to avoid.