Hi Ellis, I just recently went to the iPhone and have the 4s model. My neighbor has the 3 series and he says that mine operates much faster. I'm guessing he's referring to the response to screen taps, swipes, etc. Haven't used Siri all that much but it does seem to be very helpful. One thing worth mentioning, there is a pretty cool App called Vocal that has just been released, it's in two parts, one on the iPhone and the other on your Mac (Mac Only It seems) it will let you dictate messages, run iTunes, etc. from the iPhone. You must have the 4s for this to work. I have no affiliation with the developer.
Kevin in CT