I've used CCleaner for a year or two, and I swear by it. You're right, it's quite conservative, so it's always been safe in my experience. I run the Issues module once a month or so, and I just let it delete everything it throws up - the first few times I was cautious, and did check through to make sure there was nothing that stood out as possibly problematic. I haven't had a single problem in all that time. It's one of the first things I install on any computer I work on.