The reason I'm not using 2FA right now is twofold. First, because Google doesn't have half of their services using it for some undefined reason (for at least a year plus!). Also, the whole "app specific password" thing is a huge pain in the ass. (And appears to randomly stop working on say, IMAP mail).
Second, because the mobile authenticator is not feasible for me right now. I do a lot of android development work (well, mostly screwing around, but we'll call it work) on the side, with the result that I'm wiping my phone for romflashes at least once a week. Makes everything going through a mobile app a little useless.
I really wish Google would support a hardware token of some kind.