For those of you wondering what a 600mhz speed boost will do for the new iPhone here is your answer. This is about the iPod touch yes, but the hardware is similar (duh) so the comparison is valid.
http://toucharcade.com/2008/11/23/2nd-generation-ipod-touch-faster-than-iphone/
With that in mind, I'm keeping my 3G for another year.
http://toucharcade.com/2008/11/23/2nd-generation-ipod-touch-faster-than-iphone/
The most clear difference is that fact that the iPod Touch's processor was quietly boosted to 532MHz (up from 412MHz) with the 2nd generation model introduced in September. Meanwhile, the iPhone 3G, Original iPhone and 1st Generation iPod Touch continue to run at the original 412MHz. Though not the intended purpose, this video from Handheld Games Corp shows that the app load time of the 2nd Generation iPod Touch is notably faster than the 1st Generation model.
With that in mind, I'm keeping my 3G for another year.