No real pattern of when people do and don't upgrade. At this point, there are many applications that do not support Jaguar (two versions ago), so very nearly everyone uses Panther or Tiger. But there are a good handful of Panther users.
I'd say, if you don't see compelling features....
1) Wait and see once it comes out if something about it ends up interesting you.
2) Wait for all your apps to be 100% supported on it.
3) If you still don't want it, just skip until you have an app that will not run on the version you have.
I don't have immediate intentions of getting Leopard, but I might at some point.