Of course I don't eat fish and meat together (it's why I get upset when I see supposedly kosher recipes that call for worcestershire sauce on meat (hard to find that sauce not made with anchovies). I do cook fish with cheese (tuna melts, for example), but never with fleishings.
I have never understood what the "sakana" was, and it would be worthwhile for tabbanim to explain that to us. When something is done for a reason other than "Hashem commanded it," it is helpful if the reasoning behind it is clarified. Otherwise we run the risk that someone will say that the sakana existed then but not now, so it's not shayach anymore. That may or may not be true, but it helps to let people know what is behind the halacha, the minhag, the chumrah, the whatever. What was the sakana then, and why is it or is it not sakana now?