Depends on how you are using poser i guess. If poser is your main 3d app then the latest versions are of course the best, they have more features, the renderer is more advanced and you can use it more effectively. But if you mostly import poser stuff into other apps for rendering or whatever, then you lose a lot of the benefits of poser 5 or 6 IMO. The extra overhead of the 'advanced' features of 5/6 may even get in your way more then the 'simpler' features of Poser 4.

So i dont think you can actually call it 'living in the past', more like 'using what suits your needs and budget.' In OS terms the analogy would be sticking with XP cause you dont really need Vista as yet :)