Evaluation: 
Conclusion: performs wonderfully!
Review: I recently bought the PT-018 for use with my C-750UZ, and have now had a chance to try it out in the ocean. It works great!
The pluses are - you can take your camera underwater at the lake or the reef (obviously), or take it out in really bad weather; every function of the C-750 is available for use (including POWER ON/OFF, contrary to another review); the weight that comes with the housing nicely counter-balances the camera, so it doesn't seem to want to float or sink; land-based shots are still possible with the housing on.
The minuses - the manual is warning after warning after warning, followed by test procedures (probably a good idea, but it's BORING); one of the warnings says to not toss the housing & camera or jump into the water with it, which might sometimes be impossible to avoid; the o-ring seal seems sensitive (per the directions) and sand, grit or hair (!) may cause the seal to fail.
Overall the product performs just as you would want it to. I had the camera in it for 8 hours, and 3 of those it was submerged, with no fogging, and the camera stayed completely dry. It comes with a spare o-ring, grease, and silica gel packets, but you'll want to order more if you're going on multiple dives. (I bought my extras at Adorama.com)
Some of the actual pictures I have taken may be seen at http://community.webshots.com/album/53326052xgZpId - they are the fish photos, and have been minimally adjusted with Adobe Photoshop Elements 2.0, which is also available on Amazon.com.
I highly recommend this housing if it's in your budget, and you wish you could take your C-740 or C-750 underwater.
Evaluation: 
Conclusion: larger than it looks, but it works
Review: The case works, but it is considerabley larger than it looks on-line. The construction is solid, but the buttons seem to stick out a good distance, and I am afraid that eventually they will break off.However, the thing has a great solid feel to it.
The one, major, drawback is that you have to turn the camera on, place it in the case, seal it, and then wait after every shot for the thing to go into stand-by... in short, your battery does not last nearly as long as in normal use.
If you buy this case for the sole purpose of going under water with it, then you have purchased a good product. I thought that it might be good for storage and everyday use (I work in the jungles and high mountain areas of Peru and Bolivia, in very adverse conditions), but it looks like I might have to shelve the thing until my next dive trip.
