If it ain't broke, don't fix it!
I had no real issues with Vista, but decided to go for the prerelease offer of Win7 HP for £45 anyway

. OK so I work in IT and like to keep up to date with the new OS and was running the Win7 RC anyway before the official release, but IMO as I had no issues with Vista there are very few advantages in general use with Win7. Therefore I would probably stick with Vista and save a few quid on the new OS. But then again the preorder copy of Win7 is the full retail version so I can always delete it from my PC and install it on another if required and just move everything back to the Vista boot ( I dual boot Vista & Win7 now, but haven't been back to Vista since getting everything copied across

).
The one advantage I did have with the upgrade is that I am now running a 64bit OS and if you do decide to upgrade I see no advantages of staying with a 32bit OS unless you don't have 64bit compliant hardware - none of my older software has any issues with Win7 64bit.
Mark.