I believe I read sometime around when the iPhone 3GS or 4 came out that the average iPhone user was using about 250-400 MB of data per month. Certainly in that ballpark and I would expect even lower in 2008. I honestly don't see the average person seeing a dramatic time savings for a few hundred MBs on 3G Vs EDGE over an entire month. Also that came at a price: data went from $20 to $30 per month with the 3G.Going from edge network to a 3G was a pretty big change for me. I couldn't imagine still having the V1 and edge
I would say the 4S is like the 3GS in that there is true hardware change under the hood--and with that new features not possible with its predecessors.
Had the 4S come out in late June or Early July I think I would have been more impressed. But with the extra-long delay, iPhone 5 rumors (not that they are Apple's fault), and high expectations I believe it was a perfect storm for disappointment.
I'm really hoping Siri is all that.