What if you built a Web site for the Super Bowl, but nobody cared? For at least one marketer on Super Bowl that appeared to be the case, judging by the number of DIGG endorsements the site got. Like obsessive, hyperactive consumers Sunday evening, we surfed to every Web site that linked up their TV ads to a Web or cell phone initiative. The majority of Super Bowl ads did link to a Web site. Some were well-integrated, with chances to register, compete for prizes, text for free stuff or otherwise play around with the brands. Here’s a rundown of the most interesting stuff we saw.