When I built a new box I could pay extra for XP (full price) OR get 7 for 20 bucks...
I took the 7 and never looked back.
Now I have 7 and my theory is it works so there is no need to upgrade to 8...
I don't need the newest latest thingy. I'll look at 9 eventually I am sure but right now I have lots of 7 discs unopened so I am good for awhile.
I would never upgrade my OS to a major release. FPs and SRs sure, but like you said, it’s working why mess with it. This machine I’m at is less than a year old, given how long I keep computers I’ll probably be deciding between 10 and 11. Though I’ll definitely wind up dealing with 9 at work, as a test environment if nothing else.