Recent correspondence suggests that Poser likes things big - when it comes to Firefly renders, anyway. But it's a good question. I made a plane 1,000,000 Poser / OBJ units on a side, using UVMapper. It imported and rendered fine in Poser 4, but I had to dolly back a bit to fit it all in. :) That DollyZ value is 2,000,000 by the way - it wouldn't all fit in the dial.