What about octopus?

Just curious to know if anyone reading this has ever kept octopus. It's not something you see very often and it's something I don't think I've even ever seen in anyone's collection or at a pet store. Anyone have any insight?

I have not kept them personally, but I know people who have. They are an interesting, curious, and very predatory captive.

Some friends of mine lived at the beach and commonly caught things from the ocean for their home aquarium. We used to search the jettys for crab and small conchs and when they caught small fish they'd add them to the mix occasionally releasing specimens as they outgrew the tank then replacing them with new additions as they were found.
One day in the jettys they discovered two small octopi they were stranded in trapped pools when the tide went out, and decided to take one home.
The octopus made himself right at home in the tank and thrived, proceeding to devour every last inhabitant. They wound up taking him back to the ocean, since he obviously would have to be housed singly.

One factor to consider however is that they are prone to exploring outside the tank. They can survive for a time out of the water and can escape through any gap or opening.
I recently saw a television program where they had two acrylic tanks set up connected by a clear pipe either 3/4 or 1" in diameter. There was a very large octopus in one side, head at least as large as a basketball and they introduced food into the other. The octopus proceed to crawl through the pipe with absolutely no problem.
Truly amazing creatures. Small varieties are available in the pet trade often priced between 50 and 100 dollars.