A regular of the CR Forums has posted a mini review of the PowerShot S100. He's taken the time to post some comparisons against the PowerShot S95.
A Snippet from the review:
Overall, I’m really pleased with the S100. It will be good for all of the things my S95 is good for…and do them a little better across the board. The frame rate is faster, it seems to focus more rapidly (still slow compared to a dSLR), but in particular the dramatic improvement in ISO noise means not only better low light performance, but also higher possible shutter speeds in brighter conditions.
Canon PowerShot S100 @ B&H Photo