Actors having real sex in art-house movies. Erstwhile child star Lindsay Lohan appearing barely clad on the cover of her new album. Teenage girls strolling down Main Street USA attired in ''Porn Star" T-shirts. A bikini-wearing Jessica Simpson bumping and grinding in the music video for ''These Boots Are Made for Walkin.' " College-age women flashing for the ''Girls Gone Wild" video series with nonchalant exhibitionism. Not too long ago, pornography was a furtive profession, its products created and consumed in the shadows. But it has steadily elbowed its way into the limelight, with an impact that can be measured...