I was testing the new little Nikon Coolpix I got with a gift card my nephew gave me for Christmas. It isn't the greatest camera but it does fit in my coat pocket. If I work around its limitations I think it will be a fun camera to just carry along when I don't want to lug around the bigger Canon SX10.
You should look at mirrorless camera's (I'm looking at the Panasonic GX1 right now). There have been predictions that they will eventually do away with DLSR's. The Leica (yes, I know it's way too expensive) m9 is a full-frame digital camera. It can't necessarily fit in your pocket but camera's are getting smaller and better. I think Sony is getting ready to release a very small full-frame camera but again, it's going to be super expensive.