Perosnally, I'm sticking with the 3GS for the time being. However, the 4S looks a great bit of kit. I could certainly make use of the 8MP camera with its 1080P video recording. The Siri voiuce control feature looks very interesting- looking forward to reading some review of how it works out in practice.
If you get a 4S, please let me have your initial impressions

Cheers,
Ian