Talk about a sinkhole: According to comScore, a Web data tracker, Americans spent 302 billion minutes online last month. That's 6,760 lifetimes at 85 years apiece. Just where does all that time go? Certainly the Web has come a long way from book shopping, e-mail and porn. Just in the last few years, terabyte-oceans of video content, courtesy of YouTube, has come crashing online; social networks li