How can you tell if your wine is skunked or just crappy?

There's a fine line, in my mind, between crappy and skunked. I've seen pros miss a skunked wine, and I've enjoyed wine that some other pro said was skunked. With plastic corks and screwtops, you really don't have to worry about skunking. But save the cork after you open your bottle. If' it's brittle, and the cork seems a bit more porous and or wet than it should be, and the wine just stinks, you've probably got a skunked bottle on your hands.