i remember seeing a tutorial that showed how you can have maya automatically swap out models depending on how close the camera is to the model. in the tutorial they used a lamppost - so when the camera was close to the model, it would be a highpoly version, when it was a certain distance away, it would be a mid poly model and when it was far away it would be a low poly model.

i'm pretty sure it was a free digital tutors lesson that i got off of itunes - so it might be worth checking out their podcasts.

hope that helps.