Honestly, for a normal user, I see no reason to move away from Vista. Since SP2(and partly SP1) it has been a very good OS, especially now that hardware manufacturers have had time to get proper driver support out. I would say XP users have a compelling reason to move to something newer though.
While I agree Vista has worked well since SP2, I think its still worth having 7 for the following reasons:
- Product support. It's Microsoft's current OS and Vista is not being sold any more, so support will tend to be that much better for 7 and the difference only increases with time
- Better security
- 7's GUI is tangibly faster and snappier than Vista's, especially on lower end PCs
- The GUI has some nice improvements over Vista. Sure, not worth upgrading just for this, but it all helps
- General under the hood improvements. One may not realize them explicitely, but they are still providing a benefit
- Uses less RAM. However, with the retrofit of DX11 onto Vista, I don't know if that's still true