http://www.dpreview.com/reviews/q209waterproofgroup/
Bottom line is that the Canon is the biggest and bulkiest but takes the best pictures. The problem with the Olympus cameras is both power and shutter lag.
This review doesn't include the brand new Sony TX5 which looks sweet.
All of these "waterproof" cameras have had reported leakage issues. You have to treat them quite gingerly as their seals seem to be quite delicate. You gotta rinse them in thorougly FW and completely air dry each time you dunk them because SW will destroy the seals in no time.