I use both, Poser and D|S, although not the advanced version. I've invested too much time in learning Poser's lights and materials to switch over, I can write some Python scripts without consulting the manual and I have a working dynamics system, which I can use for every model I want. I like the new render speed and IDL - even if it will show it's full potential most probably after SP1. 

In Studio, I like the much easier workflow in posing a figure, and the setup-tools, especially Morph Loader Pro. But I did not manage to get anything good looking out of it yet - I assume I would have to buy some shaders and light plugins to get things done. At the moment I don't see a reason why I should learn this, though - buying a big application like Cinema and rendering with a render engine like AR3 or VRay sounds more promising. But at the moment I accept what I get from Firefly, until I have money and time to change. 

About the previous Poser upgrades - Poser 6 brought IBL and AO, Poser 7 a big speed improvement in Raytracing - and the ability to use multi-cores. Then there is  the morph brush, which I do use a lot for small fixes and support for HDR textures. The upgrade to P7 was worth every penny, and I'm sure P8 is worth even more. Let's talk about this in half a year, and I'm sure that the Python extensions in P8 will be a much bigger advantage as they seem to be right now. 

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.