Here's what I personally took into account for when I decided to go to the Sea and Sea...
1. Cost - I'm not entirely sure that the housing itself is going to end up being more expensive than the equivalent Ikelite. From what I've heard, the Ikelite housings with the aluminum backs are going to run somewhere around 30-50% more than the older version, which would put them at roughly the same cost as the Sea and Sea. The ports are definitely more expensive than the equivalent Ikelite versions, so overall cost might be marginally higher for S&S, so the advantage is to Ikelite, but not by a whole lot.
2. Availability - the fact of the matter is, unless you want to do a custom Ike housing for the D100 or D60, there's no Ikelite housing for either camera. I weighed the pros and cons of going with the Sea and Sea, and it was an extremely difficult decision, but I wanted to get my D60 housed quicker than I could if I chose to wait for Ikelite. When and if I decide to upgrade from the D60 down the road, I'll go through the same process again most likely.
The Sea&Sea is a nice housing - no doubt about it. If one had been available for the S2 when I bought that I would have taken it over the Ike.
I had to send my housing back to Ikelite for some repairs/adjustments and had a chat with one of their guys there today.
As far as I could tell the new custom back for the housings is more for Ikelite's benefit than for ours. It will allow them to use their MD-digital housing on multiple housings easier - mainly because it will be simple to move the window over the camera LCD to wherever the hell the manufacturers wants to put it on their camera. Basically it will make it easier for them to make housings for all the D-SLR's much faster (good thing)
Sea & Sea - ports and housing are much more expensive than Ike - I can get the Ike housing plus a couple of ports (flat and dome) for right around $1,500. The Sea&Sea housing alone will be right around $2,000 so I would say that it is much more expensive.
I'd never do a custom housing - especially when there is a manufactured housing available. Not worth the hassle and there is no camera so much better than the others that is would be worth the time and effort. If I had a D100 I would personally have gone for the Nexus, then Sea&Sea, then Subal and Aquatica in about that order...
I never really looked into the D60 so no clue what is/isn't available B)
Ike has four huge pluses in my opinion:
1. Time to market is faster than others
2. Their service department is awesome
3. I love their strobes
4. Cost makes them more affordable
The other plus for me is they are in the USA so it is easy for me to access them.
Disadvantages:
1. Size. Big and heavy on land - in the water it doesn't matter
2. Their port system locking system scares the HELL out of me. The two snapping clips - no matter how good they are - don't feel safe - and they actually allow the port to move slightly. That can;t be good for the optics. Give me a screw in system please!
3. Those big handles and strobe arms. Thank god for TLC/ULC arms.
4. I have had to use their service department (but that is mainly my own fault)
Btw, I took my Ike housing for the S2Pro down to 200fsw in Cozumel on Mariacabo - no problem at all!
Just my $.02
M