Face it, it's not terribly difficult, once you get over any mental reservations she has, for a girl to let some guy stick a dick in her mouth for a few minutes, her pussy for a few more, maybe her ass for a few more, and then sit on the floor while he jacks off on her face. And a lot of performances reflect just how easy it is.
Less common, though I wouldn't say it's uncommon, is a porn starlet who flat-out knows how to suck and fuck. (Four examples off the top of my head: Ashlyn Gere, Julia Ann, Jenna Haze, Katsumi.) Even less common is the newcummer who knows what she's doing from the first time a porn director says, "Action."
Sasha Grey is a good example. Tara Lynn Fox seems to know what she's doing, too. Who else, among the relatively younger set, do you guys think came into the industry and seemed to be just a natural-born good fuck?