I upgraded from Vista to Win 8.1 last month
It's better. You could argue that's like watching only odd numbered star trek films, but I use win 7 at work, and there's really not a problem with win 8.1 compared to that either. Its way faster than both Vista and Win 7, it's stable, and it runs everything I want to. Can't complain about it.
Worth upgrading from 7 - no. However when you're on Vista (or as someone suggested they were, still on XP) it's not only a better OS, it actually runs stuff you need to use nowadays. In my case the forced upgrade came from needing to use Visual Studio 2012 (will not install on Vista). I can see why 8.0 was hated, but 8.1 is really quite smooth.
The only annoying thing for me is that other people with these high res laptops are automatically being put into 125% dpi scaling which is making my job as a developer way harder (admittedly, I should have accounted for it, but wpf is not really helpful with that and I thought I could get away with it).