i.TV said today that it's acquiring GetGlue, the social TV pioneer whose app lets TV viewers "check in" to shows they're watching. The buyer is known for its namesake TV-guide app among and, in the business-to-business space, for powering second-screen products for brands including AOL, Entertainment Weekly and Nintendo.

The terms of the deal are not being released -- and both companies are privately held, so they won't have to report them anywhere -- but late last night i.TV founder-CEO Brad Pelo told me that "the GetGlue investors are coming along as part of the deal," meaning they will now acquire equity in i.TV.

The scuttlebutt in the tech community for much of the year has been that GetGlue's investors -- which include Union Square Ventures, Time Warner Investments and Rho Capital Partners -- were impatient and looking for a new exit in the wake of the January collapse of a deal that would have seen GetGlue being acquired by social-TV check-in competitor Viggle. That deal, which hinged on Viggle securing financing that ultimately didn't come through, would have meant a $25 million payout to GetGlue, plus 48.3 million shares of Viggle stock (the company is publicly traded), which were worth roughly $50 million at the time.

The ill-fated Viggle-GetGlue plan was to have GetGlue Founder-CEO Alex Iskold stay with the company, taking an executive position at Viggle and joining its board of directors. Last night Pelo told me that Iskold is leaving GetGlue upon its acquisition by i.TV. I reached out to Iskold and this morning he gave me a prepared statement by email saying that "Pelo and his team at i.TV have synergetic vision, and I look forward to seeing the next iteration of the combined products."

Pelo told me that his company and GetGlue began to get serious about doing a deal about a month ago, and that there were "really two core reasons" why he wanted to proceed with the acqusition: "One is that we view the GetGlue audience as being the most engaged second-screen audience. These are the fans who talk about television, and since most of us are lurkers in the social world, there is a great deal of value in those who want to contribute. As we bring them onto the i.TV platform, we think that they will generate a lot of value for all of our partners across the board. And then the second reason is that they have perhaps the best established long-term relationships with the broadcasters."

GetGlue has 75 such partnerships with broadcast and cable networks ranging from Fox to the Hallmark Channel; it also partnered with Hulu in September as Hulu sought to promote its original content.

In a press release announcing the deal, i.TV said that GetGlue has "over 4.5 million registered users." Last night, I pressed Pelo for the more relevant number -- monthly active users -- and he put that number at 1.2 million, which underscores the challenge that GetGlue, and all consumer-facing second-screen apps, face: How to gain scale.

In fact, in the interest of full disclosure, I'll note here that in the fall of 2011 I set up an informal editorial partnership between Ad Age and GetGlue, which resulted in AdAge.com publishing a weekly TV check-in chart. In late 2012 we discontinued the GetGlue check-in chart precisely because the numbers for individual shows simply weren't growing, over time, at the rate we'd anticipated; it was rare for a single show to break the 100,000 check-in mark. What started as a niche phenomenon remained a niche phenonemon.

GetGlue has since switched to reporting a broader metric -- "total activity" (which includes check-ins and other actions) -- on its in-house blog. In its report on the week of Oct. 28-Nov. 3, it lists 10 scripted broadcast and 10 scripted cable shows. None of the broadcast shows exceeded 100,000 check-ins, with "Supernatural" topping out at 93,725 total activity and the tenth-place show, "Grey's Anatomy," scoring only 30,847. Among scripted cable shows, two shows -- "The Walking Dead" and "American Horror Story: Coven" -- exceeded six figures (with 142,706 and 129,507 total activity, respectively), but the numbers quickly dropped off from there, with the third-place show, "Sons of Anarchy," scoring only 37,509 total activity.

But Pelo told me that he sees great value in GetGlue's core users, and that "while we're very interested in growing the GetGlue base, we also want to be true to what the base is intended to be, which is sort of a superfan community, and that isn't everybody. But we believe that if we can feed that superfan voice into the platform that it generates lots of new opportunities for all the partners, and that's where growth occurs."

In other words, i.TV seems to recognize that those inclined to be highly active in the social-TV space are a relatively small group -- but that leveraging the collective voices of those highly engaged users has the potential to excite and activate a larger base of social-media "lurkers," as Pelo calls them. Amplifying those voices by deeply integrating the GetGlue and i.TV platforms is the game plan.

Pelo and I spoke further about some of his plans for GetGlue; stay tuned this afternoon for a follow-up post.

UPDATE: 'Why We're Buying GetGlue': A Q&A With i.TV CEO Brad Pelo

Simon Dumenco is the "Media Guy" media columnist for Advertising Age. Follow him on Twitter @simondumenco.