Christopher Nolan spoke about the downside of shooting IMAX after TDKR came out. I'd been hoping and praying he would have shot it all IMAX so was glad of the explanation why he couldn't.
He talked about it being less a case of cost and camera size. The cost is negligible with the kind of Blockbusters IMAX is used for and the cameras are getting smaller all the time. Also the spectacular image quality makes it worth putting up with those problems anyway.
The big issue is that they are VERY noisy making recording live dialogue impossible. So far an action setpiece when you are going to dub everything in post anyway it's no problem. But for intimate dialogue scenes it would mean getting all the actors to post-sync their performances, which is usually a bad idea (Unless you're Sergio Leone!).