hell no I'm not getting them. I got bored of Halo 3 multiplayer achievement whoring and stat building already. I'd be a lot more tempted by new campaign levels since the co-op is awesome.
the multiplayer mode doesn't lend itself to constant ranking up that well. you don't get anything. maybe in a couple months when they're free I'm going to try and get all the achievements so I can get the samurai gold armor with the sword again.