On my personal desktop, I have 96gb... I've never gone over 70 or so.. but that was with a lot of services running a fairly complex system with data loaded locally. I generally don't five a f*ck about the ram I'm using day to day. I'll run various updates and reboot between once a month and once a quarter.
My main machine has 16Gb of RAM and I don't think I've ever seen it go over 4Gb and that was when I had a 200gb mmap'ed sparse array.