The copying process was never that much of a big deal, but paying for 8GB of graphics ram really is.
I don't know about that? Texture memory management in games can be quite painful. You have to consider different hardware setups and being able to keep the textures you need for a certain scene in memory (or not, in which case, texture thrashing).
Using Intel's integrated video as a way to assess the benefits of unified memory is off target. Intel had a multitude of design goals for their integrated GPU and UMA was only one aspect so it's not so easy to single that out for any shortcomings that you seem to be alluding to.
You also have an (estimated from die shots) 64 megabyte SRAM system level cache and large L2 and L1 CPU caches, but you are indeed sharing the memory bandwidth between the CPU and GPU.
I'm looking forward to these getting into the hands of testers.