I have made it a habit now to work with 8 about half of the time. I installed most of my programs that I usually use and there was only one program that refused to operate as expected.
What impresses me is the stability of the system. Despite some rare unexplainable little glitches, this system does everything smoothly. This is really amazing for an Alpha test version. Since I was an operating system developer myself for over 35 years, I can really appreciate the quality that the Redmond boys delivered. They are far better than we were in my days.
Nevertheless I think the UI is somewhat "bulky" on the PC. You have to click on more things than one would expect to do simple things and certain functions are hidden so badly that they are difficult or impossible to find. This is not a critizism of the Metro UI in general, but an observation as to its applicability on a PC.
I generally I like to discover new things and a new system does not frighten me. But in the current state, I would probably not use 8 on a PC - the operational characteristics of 7 are a lot more elegant on a PC. For a Tablet though, I think 8 will easily be favored by people used to Windows.