For whatever reason, I sort of love this headline on Decanter's website—"Americans 'Baffled' by Screwcaps." It summons images of, I don't know, a bunch of thuggish guys (the cast of the sadly now-no-more Sopranos would work well) sitting around a screwcap-sealed bottle, scratching their heads and saying things like, "I dunno—hey, Louie, you know how to open one of these?"
Hard to believe, except that I've actually had conversations with more than one retailer about people returning screwcap-sealed bottles as defective, because they tried to open the thing with a corkscrew and ended up, after heroic effort, puncturing the top of the screwcap.
However! I will pass along a tip from a Australian sommelier I met once—those Aussies are very experienced with this whole screwcap business—about dealing with recalcitrant screwcaps. To wit: grip bottle in one hand, grip the collar of the cap-thing (i.e. not the top itself) in the other, and turn in opposite directions. Tends to work well, I've found.
Of course, pliers are handy, too.