Don't you find it gets slow?
Well, I'm running Linux, so let's see. Viruses just aren't an issue as long as you're sensible. XFS never needs defragging. CCleaner is pretty unnecessary even if it did exist for Linux. And there's no registry to get corrupted or stuffed full of crap. As for disk cleanup, I haven't got anything leaving random rubbish all over the place so why do I need it?
Starts up and runs as smoothly as the day I installed it (couple of years back.)
That said, on my Windows machine I still don't do a lot. Being windows I wipe / reinstall every year or so as a matter of course and it doesn't see heavy usage, so I've never run into any registry issues / fragmentation problems. Unless you're doing something seriously wrong, your weekly actions are most likely overkill!