Missed flying over all the fog this weekend, but it looks like I'll have the chance in the next few days still!
Great fun, but as others have said you need to be careful to make sure you know where you are and have an escape plan.
As for "clear of cloud and in sight of the surface" surely that means exactly as it says. As long as you can see some of the surface, whether a hill in the distance, or down through some holes thats good enough, legally.
Yes, if your engine stops, you have a problem, but you also do flying in the mountains or over the water or even over a large forest.
Those that think they are better off flying with an IMC rating or IR over the fog I think are mistaken. Thats not going to make much difference if your engine fails and anyway, the fog is probably below the minimums for your rating anyway. The only advantage you would have with such a rating is if your plan wasnt so good and the fog moved leaving you with nowhere to land VFR. Of course again assuming that somewhere with an approach procedure was above your minima!