ce4jesus has it about right.
My wife and I have been using Olympus housings for abot 3 years. They're cheap and easy to use but you have to police the o-rings without fail. I think the Ikelites may last the life of the camera. You should expect the Olympus housing to be disposable unless you have it serviced, (the service may cost more than a new, shiny housing). So it might be a good idea to buy a spare if you plan on keeping the same camera more than 3-4 years.
You can get the Olympus housings for ridiculously low prices. I just bought a spare, brand new, PT-020 for $70 US.
We both have the Heinrich's adapter and bulkhead replacement. The metal bulkheads are far less prone to problems. The combination has allowed us to use inexpensive, used, Sea & Sea YS-60 strobes bought off eBay for under $200 US. She has two connected with an old Sea & Sea dual TTL adapter and they work fine for wide angle.
I've used the SP-350 on two trips while she has stayed with her trusty C-5060. The SP-350 is a really nice camera for the money, ($199 at Costco this week!), but it is frightfully slow at writing the pictures! It's not an issue for what I shoot but it would never work for the wife's fish and tortoise portraits.
I always think about a super fast SLR and then I look at the $1200 housings. Yow!