Preview at WWDC likely in June, followed by September launch.
iPhone 4S Geekbench Benchmarks ~68% Faster than iPhone 4
The listed specs show a dual core processor that resembles the results from from the iPad 2 which also shares an A5 processor. Free RAM appears to be in-line with what we believe (512MB) and the benchmarks line up with known devices.
The iPhone 4S receives a total Geekbench score of ~622. This falls slightly below the iPad 2 scores of 749, but well above the iPhone 4 benchmarks of 370. So, the new iPhone seems to benchmark about 68% faster than the iPhone 4, and about 17% slower than the iPad 2.
The iPhone 4S A5 processor is likely underclocked (800MHz) as compared to the iPad 2 processor (1 GHz), explaining the slightly lower performance.
The iPhone 4S is currently shipping to customers for delivery on October 14th, but it seems at least a few units are already in the wild.
Update: Anandtech compiles these results (and more) in nice graphs:
Meanwhile, graphics performance of the iPhone 4S is confirmed to be about 7x faster than the iPhone 4.