That's currently my set up. iMac was my only computer for a while so I figured I'd compliment it with an iPad but quickly realized the iPad wasn't cutting it for me since my iPhone fulfills all of my iOS needs.
I sold the iPad and bought a 64GB 11-inch MBA last year but, ever since, the only times I find myself using my iMac is when I sync my phone. So, now I'm back in the same situation: I didn't need an iPad because of my iPhone and now I feel like I don't really need my iMac because I use my MBA 98% of the time. With that said, my plans are to sell the iMac and MBA and just buy a 13-inch ultimate MBA and pair it up with an old Dell 24" monitor I have, for those rare occasions that 13" won't suffice.
I love my iMac, I think it's a beautiful piece of art but it eats at me that I have such an expensive machine on my desk doing nothing but collecting dust.