Barbaracle looks like it might be very viable. It may not have the initial titanic Defense that Cloyster has, but what it does have is usable mixed defenses before it Smashes. I'll be beating the dead horse by saying that the initial post should remove ALL mentions of Nature Power and replace it with the actual Earthquake since Barbaracle can learn it through TM (GODLY thing, too. Granted you miss out on a Tough Claws boost with Earthquake, it's still nice to learn a reliable move). It definitely needs support to pull off, though. Electric, Fighting, Ground, and especially Grass Pokemon won't allow Barbaracle to sweep as easily unless it runs a coverage move to go against all of them. Ice Punch would be an interesting move to see (kind of sad that so far it isn't, yet it can learn Ice Beam and Blizzard).
Whoa...this thing has Switcheroo as an Egg Move (thanks, Serebii!)? Umm...odd move to put on this thing, so...well, it'd be gimmicky. I mean, Trick and Switcheroo work better on Pokemon like Reuniclus since they have Magic Guard, so...I don't see Switcheroo on Barbaracle anytime soon.