Wow, this is starting to make my previous thoughts about being an instructor seem like a piece of cake! A couple of things occur to me:
First, it seems that it would make sense to buy out someone else's shop, if possible rather than start from scratch. That would give you the clientele and connections right off the bat, shortening that painful period when you're making negative profits. Of course, it would probably be more expensive.
Second, I do see a serious problem with customer service in a lot of dive shops. It's true, divers and shop owners often have attitudes similar to musicians (i've met some of the worst sales people at music stores) - complacent and a bit arrogant, as Otter mentioned. I've always thought I could do a better job at sales in an industry that I love. I recently met an lds owner who had the ideal attitude - excited to speak with me, gave me all the info i needed and more, friendly, etc. Another thing that struck me about her shop was that an integral part of her business was a dive club that made really frequent trips (a more popular idea in the northeast). This shop is in Brooklyn - I don't know if that would be necessary in a tropical location where it's easier to get to dive sites and easier to get people to dive, but I found the idea appealing. Netmage mentioned his frustration that his lds doesn't facilitate local dives. The key idea is to keep people diving, and offer that end-to-end experience that netmage spoke of.
Third, I've been thinking that I might want to set up shop in California. Is diving there really year round? Or does it taper off in the colder months? When I was in Monterey this year the vis really sucked at Breakwater because of the high level of particulate matter.
I am planning on getting my instructorship first and possibly working resorts before even thinking about a shop.