Your log looks fine. I've seen the clock skew warning when I did VMWare folding, and it returned results just fine. When I fold on my 550Ti what I check for to see if the F@H is working is the heat and the GPU usage, which should be higher than playing any game
Note also there's a few nVidia drivers that F@H doesn't like. I can't find the post, but with my experience anything between the driver first released for the 550Ti and the 285 series of drivers (non-inclusive) did not work, although they failed immediately. The 285 and 295 series of drivers worked for me.