I would say that almost everything from Infini-D got incorporated in to Carrara. The Spline modeler is virtually identical except you get a heck of a better preview in Carrara and the speed is ten fold faster. There are some drastic changes, like the way you texture stuff is radically changed, but like the person that posted before me stated, I don't see you having to much of a learning curve. If you liked Infini-D, and you like Poser, you should love Carrara.