The deal for the Cambridge, Massachusetts based Bluefin Labs will be Twitter’s largest acquisition to date.

This helps to clariy Twitter’s likely future positioning and business model. The purchase adds legs to Twitter’s increasingly credible claim that it connects “second screen” viewers for ad hoc conversations during events. 

As the news broke a day after the Super Bowl, my focus was already on Twitter thanks to Marketingland’s provocative observation that 50% of the games ads included Twitter hashtags, while only 8% mentioned Facebook, and none mentioned Google+.

Twitter was a big part of my night, connecting my Super Bowl ad viewing party to advertising students on the hashtag #BrandBowl. And I tweeted remarks that Twitter was all over Super Bowl advertising.

My friend, Ron Miller, wisely tweeted back that the use of hashtags in ads only proves they are popular among marketers and advertisers. And Ron’s caution is backed up be research from ExactTarget in its “Marketers Are From Mars” report. Though marketers are different from customers, and they’re far more fixated on new media, Twitter and the second screen has beocme a big deal with mainstream audiences.

The impact of twitter and “second screen” viewing is increasingly mainstream. Here’s proof:

So, Twitter’s acquisition of Bluefin Labs was announced at the perfect time.

After all, if the awareness of second screen viewing is at a high, so its is market potential. The revenue model for the first screen is predominantly ad-based. Twitter is-lined up for an ad-driven model on the second screen, that my redeploy some of the spend focused on television.

Twitter is also in a great position to evaluate the impact of the first screen. As Ad Age asked a few months ago: If Twitter has become the new TV Guide, can it also offer ratings? 

Twitter’s business model may have seemed quixotic in its early days. But now the gang that brought us the FailWhale, seems to be lining up to be the king of connecting second screen viewers.

In the age of the second screen, Twitter has a chance to be both the carrier of the conversation about events, and the ratings agency that evaluates the first screen’s impact. That makes them competitive with Facebook, Neilsen ratings, and it makes them attractive to anyone who wants to message second screen viewers based on their momentary interest.

Klout score may rank your use of Twitter, but thanks to this purchase, Twitter will be able to rate the impact of broadcast media and global events among its users. Think of Twitter as the world’s biggest focus group, and the network connecting second screen viewers.

Of course Facebook will have something to say about this, but it may well be as a fast follower of Twitter.