As already mentioned with Poser 2010 it has 64 bit program and render support, background render, supports a slightly better range of import/export stability with files, better alpha-masking, better texture filtering.  In addition the Pro versions of Poser generally feature a slightly up-modded render engine, with richer and better lighting and faster ray tracing.  Another great feature is the Queue Manager, only available with Poser Pro - and it's not just for networks, despite what you may have heard; With the Queue Manager you can batch render multiple jobs in sequence, or render off animations while continuing to work in Poser (background render is limited to a single frame from a single job).  Also, to my knowledge, Poser 2010 Pro also features more content.

I haven't really had a chance to fully test it, I hate the Poser 8 style interface and library also used by 2010(it's hit or miss from my understanding, you either love it or hate it), so I am still doing a lot of work in Poser Pro 7.

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