I researched both the Olympus and the Pentax when I was looking and they matched up pretty close. I finally went with the Pentax based on looks and price. For a long time, these were the two choices in waterproofs, however, there are several companies that now have them out. Here is a fairly recent review of 7 that are out.
http://www.dpreview.com/reviews/Q209waterproofgroup/
This test had the Canon PowerShot D10 and Panasonic Lumix DMC-TS1 tying as the best with the Pentax Optio W60 as the runner up.