I've used Hyper-V on W8CP for a few weeks, with W8CP as a bare-metal install on my HP ProBook 4430s (80GB SSD, 320GB WD Scorpio Blue, 16GB RAM). Overall, I have to say that Hyper-V 3.0 as implimented on the client OS easily works as well, if not better than Hyper-V 2.0 on W2K8R2. Some of the changes are primarily suited toward laptops, such as the ability to bind wireless adapters to the virtual switch and the ability to sleep and hibernate. As usual with Hyper-V, you aren't going to get true full-screen with decent video unless you enable remote connections on the child OS and connect via RDP. Needless to say, you want to set the connection speed within RDP on the parent to the highest possible option. Once you get used the hot corners, switching between fullscreen RSP sessions is quick and painless. The benefit to Hyper-V when running multiple child OSes is that it's the layer on which everything runs. On the downside, even on the client OS, Hyper-V throws fits when you don't have the proper admin rights.
I'm currently using VMWare Workstation 8 on a fresh W7HP install on my laptop. I'm doing this mainly to learn the basics of working with VMWare during an MCITP course that is being followed by a VCP course. In many ways, I am starting to see that VMWare Workstation makes it easier to make changes on the fly to a guest. It also does a much better job of displaying guests, since it will fit to window size - something I wish Hyper-V did. Also, VMWare Workstation still does better at supporting non-MS OSes. One thing that Hyper-V lacks still is good Linux integration.
I think a good summary would be to say that Hyper-V on Windows 8 is good for a MS-centric environment. If you need to test patches or something you're developing, or if you need an older version of Windows to support vendor hardware, having Hyper-V on the client is great. If you want to have the newest Windows OS running on a convertible laptop or a touch-screen PC, but also want access to games that may require Windows 7, again, Hyper-V is great. If you need to virtualize Windows for a class or a lab, again, it's great. Conversely, VMWare Worksation is still carries the industry banner. If you want to test out different OSes, it will certainly beat out Hyper-V. Also, if your company already has invested in VMWare, I don't see Hyper-V neccessarily taking over. On the other hand, if you don't currently have a virtualization solution in place, Hyper-V will leverage your existing infrastructure better, since it's an "already there" feature.