Matt - it looks like you and I are the first two to get the 20D housing! I've just assembled mine today. I'm still getting used to Ikelite as my only experience with SLR housings has been the Nexus for my Nikon n90s.
My first impressions, both pro and con -
1) I'm no longer concerned at all about the fact Ikelite is a plastic housing. It's a VERY solid chunk of plastic and seems as bulletproof as any aluminum housing. While it doesn't fit the camera like a glove like the Nexus does the N90, it's still smaller than some metal housings.
2) I like the transparency...a lot. I like being able to inspect the o-ring after closing the housing.
3) Installing the camera is much easier than in the Nexus. No fiddling with knobs and aligning gears. Everything just falls into place. Nice!
4) I'm not comfortable yet with the port system - it seems a bit loose. I can still wiggle the port around after it's been secured. Is this normal? Both ports that I ordered wiggle a bit when installed. I do miss the screw-in method of the Nexus, which seemed more secure.
5) The housing was certainly fresh off the production line - it was covered in plastic dust left over from the machining/drilling. Took a while to wipe it all off, and I'm paranoid that some of the dust has made its way into the control glands and will cause trouble 100 feet down.
Time to go to bed now - will test some shots in the bathtub tomorrow!
Ben