ScubaSteve
Wow.....what a DB
Although the Canon housing is significantly less than the Ikelite, there is definitely a huge difference in the quality and features. Ike's extremely durable housing build, better controls, and of course the TTL functionality, makes the Ike housing a much better choice. Budget is always a decision factor, but in my eyes its worth waiting to save the extra few hundred so you do it right the first time.
I'll second the 'Pros comments. I started with a A570IS in a Canon housing, and less than a year later I find myself with the housing and camera replaced with a dSLR system and a new pair of DS-125 strobes. I could have saved a bit by starting with the good stuff.
While I agree that you can save some money by "going for the gusto" immediately, I see absolutely nothing wrong with investing a bit of money on a WPC housing and learning to shoot underwater. I started with an old 5.0mp Canon and a Canon WPC housing and loved everything about it. It took me two years of shooting that before I decided to invest and upgrade. I still have the old one as a back up or for my GF when she dives with me. I see nothing wrong with starting small and working your way up. It does cost you money in the long however you are able to grow your UW photography talent with your equipment. You are also able to stop when you are comfortable with what you have rather than spending all your money on something that you may not use all the time.
Don't get me wrong, I am not arguing to stay away from the higher end systems but just that there really is nothing wrong with learning and starting on a smaller system. I think people need to know how serious they are before they make the full investment (just my opinion). In fact, I wish that I had started with a full system up front but I know of at least one person that went all out and then became a vacation diver. Ooops.