Social search is an interesting animal, mostly because there are so many different approaches. There’s realtime search, like we’ve seen from Google+ and Topsy in the last week. There’s Google’s social search, which simply sprinkles social results throughout its web search results. There’s the Wajam/Greplin approach, where you give the services access to your account so you can search through your social networks for relevant results.

Popular URL shortening service bitly has announced its version of social search, and it’s more about searching through popular content.

“bitly shortens 80 million URLs every day, give or take a few,” the company says. “Now, with our new search technology, we’re crawling and classifying every URL we shorten to create an index of the most ‘viral’ content on the web — content that’s broadly distributed, frequently-clicked, and trending at a high velocity.”

Bitly shares an example of a search for “onstar” comparing it to a Google search.

Bitly points out that there’s been some controversy surrounding OnStar tracking its customers, and that the top results here show news stories about the company and a blog post from a person talking about it, and that a Google search returns the company’s official site and its Wikipedia page – “results based on Google’s pagerank algorithm, which prioritizes the pages which are linked to by the most authoritative sites on the web.”

To be fair, when I searched Google for “onstar” the first two results are as bitly says, but the next one was an Engadget article about tracking. There are also several other first page results on the tracking topic, and the company’s Facebook and Twitter accounts, which in all honesty may be among the results a person wants if they just search for the “onstar” query.

“This is the challenge of the realtime search space — many of the pages are so new, so fresh, that they don’t have any pagerank,” says bitly. “A personal blog post isn’t authoritative in the way that the New York Times or Wired magazine is authoritative, but stories don’t find their way into Wired unless people like Jonathan Zdiarski [used in bitly’s example] speak out. Increasingly, they do, and often they reach a broad audience on social media before more conventionally-authoritative newsgatherers amplify their messages. ”

There’s certainly a case for realtime search. No question. I thought Google did a fairly good job of it when they had it, but then they lost the Twitter firehose, and the feature went away. Sooner or later, Google is expected to bring it back, with data from Google+ and other sources. Google did launch realtime search in Google+ this week. Perhaps that is coming closer to fruition.

Rather than using a pagerank-type signal, bitly displays stories that it predicts will get the most attention over the next 24 hours. Then it uses its own analytics to refine the predictions in realtime. “Our search technology is based on the the most valuable measure of engagement: the click,” bitly says.

Bitly has even built a reputation monitoring service around this technology, with an alert system. It’s designed to warn you about “swings in volume and sentiment related to specific keywords” in realtime, as opposed to just showing you what’s already been said about you or your brand. There’s also a dashboard (pictured at the top of the article) where you can view keywords you’re tracking. This feature rolls out to beta testers and bitly Enterprise users over the next couple weeks.