Very interesting post... I've been shooting underwater for about 10 years now, and started with (and still occasionally use) my old Nikonos V. No matter how good digital has gotten, the subtelties and nuances you get with film doing macro with extension tubes or with a 15mm wide angle can't be beat. Of course the pros of digital far outweigh the cons.
I decided several years ago to switch to video and purchased a Sony PC110 with a Light & Motion housing. The housing is very compact compared to other housings that were on the market at the time, but I had so many problems with malfunctioning lights, batteries, controls, etc. that I spent half my time underwater fiddling with the housing. I also found that, although I did get a good amount of great raw footage, I don't have the patience nor the desire to spend hours editing video footage, putting music to it, titles, etc. So the PC110 and housing are tucked away in storage and I didnt even take them on my last trip...
I did manage to pick up a Nikon Coolpix 5600 and the new Nikon WP-CP3 underwater housing... For a little point and shoot that fits in the palm of my hand, this system worked suprisingly well on a recent dive trip. It was easy to switch modes underwater, and I was able to get good wide angle shots and macro on the same dive. Of course, the built in flash doesn't illuminate anything beyond a few inches, the shutter lag is incredibly long, etc. Still, for an investment of around $500, this is a great little back-up and I'd take it when there's a chance I'd get in the water whereas I'd only lug my other photo gear on liveaboard trips.
So I finally broke down and purchased an Ikelite housing for my Digital Rebel 300D, and a dome port for my Canon 17-35 USM. I also picked up the Canon 60mm with a flat port, and have my eye on a barely used Sigma 15mm FE which will complete the system. I went back and forth between the 100mm and the 60mm lenses before finally deciding on the 60mm, and based on your comments, and the images you shot with the 60mm, I think I made the right decision. I think the 17-35 2.8 will be a good general purpose lens, and several pros I know used that lens almost exclusively on trips I've been on. It seems like a lot of people have now migrated to the 15mm FE, and given that I tend to spend a lot of time photographing sharks, I think that will be a good addition.
I went with Ikelite for a number of reasons... 1) the company has a great service track record and a lot of people have given it very high marks, 2) the housings seem to be great value for the money and cost a lot less than other housings, 3) I do like the clear housings because I'd rather see the start of a flood rather than trust a moisture alarm, and 4) I like the eTTL2 feature with the new DS125 strobes.
I did pick up one DS125 and I'm guessing I'll buy another before my next trip in June.
My first impressions of the housing (not having dove with it yet) are generally good. The packaging was great (unlike the comments you made with respect to the Subal housing and ports). Instructions were pretty good, and everything was clean and well-protected. Yes, the ports came with neoprene covers, so I guess I'm going to return the extras I purchased. Installation of the zoom clamp and the focusing sleeve on the 17-35 was a PITA. I had to shim the sleeve, the adhesive on the shims was almost useless, and the gear sleeve won't fit over the lens from the front. The control to operate the on/off camera switch isn't well designed, and while it's easy to turn the camera off, turning it back on is very difficult. The strobe arms are simple to attach to the camera tray, but the ball arms don't lock down well enough to hold the weight of the strobe. I suspect this will be much less of a problem underwater though.
I'm dying to get in the water and try everything out... I think I made some good choices, and you can't beat the price... The housing, two ports, the strobe, the 60mm lens, ball arms, chargers, etc. cost about the same as many housings alone.
Anyway - I enjoyed your post given that you went through a lot of the same thought processes I just did.