At the moment I'm working with a 190mb Moi file. all is layered and objects named, so it's easy to switch things on and off to work on them or have them in the background.

Another thing you might take into consideration: the amount of RAM that is used. With my file I'm close to 1.5gb RAM usage and I experienced some strange crashes of MoI that never occured ever before when I tried to export too many things at once via .obj. Otherwise it works as a treat and I can only say that MoI saved my ass on the current job.
As I don't see a 64bit version mentioned anywhere this might be a bottle neck in future for me - any plans to change that Michael?