I was asked why I removed my post, the following is my response. Once I finished writing it, thought others might benefit. Good luck!
Well, one my biggest initial disappointments turned out to be incorrect. After re-reading the manual, I discovered a footnote. Only in sea or ext. flash mode can one switch from stills/video/playback by pressing a certain button. In any other setting, one has to use a switch on top of the camera, but there is no way to use that switch with the housing. So before I saw that footnote, I couldn't believe this camera would be designed such that one can't switch between the settings. It is not obvious or intuitive to figure that out.
I have other issues. The battery is ever so slightly different, but enough to inhibit using the DC500 batteries. I had recently found some 1000 mAh batteries for my DC500. I was looking forward to using them in the 600. SeaLife batteries are spendy, $30. Bought two of them, so now I have three. I am skeptical if they will last as long as I need them. Not very happy with this battery switch. Think it is SeaLife's way making more money. Why make special batteries?!!?
Since I wrote the above, I found out Sealife doesn't make the batteries, and what the generic battery number is, Li40/Li42B, which are for Olympus cameras. I just bought four 1000 mAh new batteries on Ebay for a total of $33, including shipping and insurance. The shipping is where the money is being made, as the batteries were actually $0.97 each. So if you buy the DC600, I would suggest doing what I did - look for Li-42Bs.
On a power related note, the camera cannot be plugged into an electrical socket. The batteries have to be taken out to be charged. To download from the camera, have to either take out the memory card, or use battery power. The camera does come with a charger.
There is no sleep mode any longer. This could be because the start-up time for the DC600 is much faster than the DC500. I would set my 500 for sleep in the 30 seconds, but always on. It will be interesting how it dives (hopefully tomorrow) turning it off and on. So, not sure if this is good or bad. Since I wrote this, I have dove with it. I simply turn the camera off/on, and have it set to auto turn-off after one minute. So far, so good. The 650s still do okay, but haven't really given them a long dive and/or lots of pictures test. I will feel much better once the bigger batteries arrive. The start-up is really fast.
The shutter/focus button is a little on the sensitive side, at least compared to the 500. I have dove with it twice, and sometimes it take a picture before I expect it. Although, now I think I know what to look for as I am pressing the button before it takes a picture.
The camera has some cool and very useful focus and flash modes. There are three of each. One for close-up, distance, and auto. If it can't seem to focus, push the button until get distance and the camera automatically goes to infinity focus. It focuses better for close-up on close-up. I was skeptical about the flash modes, especially since my digital strobes are adjustable, but they really do work (I tested it in my home - the distance mode too bright of flash, but the auto and close-up were very similar). The buttons are much like the 500's, which are tad small for dry gloves, but pushing the focus and flash modes still possible. Oh yes, the power and shutter buttons are reversed, which is better, although, I accidentally forgot for one picture and accidentally turned off the camera instead of taking a picture. Luckily, I was able to turn it back on, and get the picture.
The bigger view screen is very nice. The brightness of the screen can be controlled.
Cannot shoot TIFF pictures, but I guess that isn't the biggest of deals. 6.1mp is better than 5.1.
Even though not supposed to use 1 gb cards in the 500, and can in the 600, I did in the 500 and had no problems. I use a very fast 1gb, something like 166x. That quickens up the shutter speed.
SeaLife does have excellent customer service. Hopefully I will never need to use them. Overall, the 600 is improved over the 500, and am glad I switched.