DWhatley is the only non-pro I can think of right now, unless you count the folks raising babies, but Carol has sometimes, and probably a few others. And a lot of the researchers and pro aquarists, like Jean, Roy, Marinebio_guy, and gjbarord, keep a lot of animals at once. I know Thales has a bunch of tanks linked together for filtration, and while I don't remember him having two octos, he's certainly had one octo and several tanks of cuttles. Just to reiterate (for people searching this thread in the future) two octos in the same tank often causes problems ranging from undue stress to cannibalism.
edit: due to brain failure, I forgot Dreadhead had 2 octos in separate tanks until yesterday () and AM had one at home and one at work recently. Sorry for forgetting you guys.
As Monty mentioned, I have 3 octo tanks. Two with Mercs and one with a Hummelincki. I plan to keep all three populated and will have a go with a Briarius if JoeFish is successful with his brood. My mercs, captive raised, are approaching the end of their lifespan but I have two captive bred that will reside in Sisty and Medusa's tank when it is empty. The larger tank was originally planned for a briarius so I hope to have three different cephs most of the time.