Do you have both cameras? I was ready to buy an S100 before the RX100 came along, and still might considering that it's half the price, but so many people seem really excited about the Sony.
Yes, and I also had (or still have but not using an S90). RX100 is not twice as good as S100, but we all know that incremental improvements on the high end cost exponentially more.
Depth of field is what makes the camera, you can get the bigger camera look which wasn't the case most of the times with the S100. That is if you don't want maximum depth of field.
At low iso I don't see that much of a difference when equivalent DOF is used. For color accuracy, WB, etc you should look for more specialized reviews.
Noise is better on RX100, we'll see when LR supports it how much the difference really is. I'm using RX100 at auto iso max 1600, the S100 at max 400. The difference might be a little less than 2 stops though.
Handling is different, it might be a matter of getting used to it. With RX100 you have to go the menus often if you like to tinker things often, but most of the settings can be accessed with few clicks only. Most of the times I use it on Aperture priority, auto iso up to 1600, I have exp com on the ring (works so-so) and manual focus -auto focus switch with the back center button (or however it's called). And few often used settings on the Fn button. I usually set same basic stuff appropriate for the scene and then I rarely change anything unless I change entirely the subject or the scene so it works OK for me.