The A5 and 8 MP camera along with Siri makes it worth an upgrade...when you can, at least. People sacrificing their current contracts and paying the fees are dumb for this go around, especially if they have an iPhone 4.
Hopefully next June sees an iPhone 5 release, but that's looking unlikely now I suppose...my contract is up in February so I guess I'll be getting a 4S around then, unless there's a new Galaxy by then as well.