Just when analysts and journalists were believing that interest in acquiring Internet advertising firm DoubleClick had perhaps dwindled, it’s Google that made the big play late this afternoon, beating Microsoft to the line in a deal Google says late this afternoon is worth $3.1 billion in cash.

The deal comes as a boon to the equity investment firm which had purchased the once-colossus, later-troubled online ad broker for $1.1 billion two years ago. Microsoft was reportedly the first bidder, in a deal that analysts believed would only have been worth $2 billion – but just a few weeks ago, that seemed like a lot, perhaps even too much.

But what appeared to be silence to some observers may have been Microsoft quietly upping its counter-offer, maybe more than once, in a round of serve-and-volley with Google that the latter has clearly won.

In a very carefully worded comment late this afternoon, Google CEO Eric Schmidt said, “DoubleClick's technology is widely adopted by leading advertisers, publishers and agencies, and the combination of the two companies will accelerate the adoption of Google's innovative advances in display advertising.” Schmidt doesn’t exactly say Google will utilize DoubleClick’s platform; in fact, he points to his own company’s “innovative advances,” which could conceivably replace DoubleClick’s without too much disturbance of its customer base.

11:00 pm ET April 13, 2007 - This afternoon’s joint Google/DoubleClick briefing with analysts did not have the characteristic Google attitude. Many queries were posted, as it were, but few search results turned up. The reason, Google CEO Eric Schmidt, was made clear right away: Although today’s deal, consummated just hours earlier, was “something we’ve thought about for a very, very long time,” neither side had actually worked out the major details.

So the degree of what isn’t known this evening is substantial – in fact, it’s perplexing, especially with regard to a $3.1 billion cash investment. The role current DoubleClick CEO David Rosenblatt will play, if any, in a company that’s already stacked to the rafters with executives, may yet be determined.

Just how Google came up with the $3.1 billion bid is just as unknown, except for the fact that it has that much cash on hand. Executives on both sides refused to answer questions about how DoubleClick was evaluated, exhausting the usual side-step responses (“We typically don’t give guidance...”) until they started just winging it: Schmidt, at one point, perhaps in an effort to fill time in search of a more appropriate answer, explained the two companies happened to lease office space in the same New York building (the Caledonia on 17th Street and 10th Avenue), implying that since they were neighbors already, they concluded they may as well be family...and that was where the two companies saw the value.

“One of the things that we hear most from our customers, both in the online world and the offline world, is specifically around making the process easier,” responded Tim Armstrong, Google’s vice president of advertising sales, to the $3.1 billion question, “and in general, we feel that a key outcome in the industry right now is operationally improving the underlying connections between advertisers and publishers and agencies. Certainly we see a clear path online. I think the same is true in the offline world as well.”

Another question: Has the deal been run by the Federal Trade Commission for guidance yet? Google vice president and general counsel David Drummond audibly stalled for time, uttering random phonemes before answering that this is the sort of thing merging companies generally do, so they indeed plan to do that.

The merger process, we did learn, could consume most, if not all, of this year. As Drummond explained, “We expect the transaction to close sometime later in this year, subject to the regulatory requirements. Until that time, DoubleClick will operate as an independent company.” The question to which he was responding was, why will the process be completed late in the year; essentially, he confirmed the premise without repeating it.

Why do the deal now? Why didn’t, for instance, Google acquire DoubleClick back when the asking price was closer to $1.1 billion – the price investors Hellman & Friedman paid for it in 2005? “The reasoning from a Google perspective,” stated Eric Schmidt, “is that DoubleClick has been a partner of Google’s for many, many years; and as I mentioned, people knew each other and they talked to each other, and...they were doing a very good job in the display ads business, and we were actually focused on some of the other ads businesses. When we did a strategic review for this year, we realized that the scale of the display ads business was much larger than we had thought, and that the DoubleClick management team, frankly, had done a very impressive job of entering that business and growing it. And that was a change of view, an understanding now of how much larger an opportunity it was, and how it could be targeted...We’d had informal chats before, but the alignment wasn’t there, and we got to the alignment now.”

This was one of the more informative responses analysts heard all afternoon. Based on that, one could come to the conclusion that DoubleClick’s management team was what appealed most to Google’s.

But contrast that explanation with the prepared statement read by Schmidt just minutes earlier, as he opened the conference from on location in Argentina: “From our perspective, DoubleClick is in a unique position to strengthen advertising and the advertising business of Google. More importantly, we think this benefits advertisers, partners, and end users. The first, and in many ways, most compelling argument for this from a Google perspective is that it’s accelerating our display advertising business. By virtue of both acquisition and the subsequent integration of tools and technologies between the two companies operating as one, we’ll be able to offer integrated tools to solve interesting problems. And more importantly, perhaps, people will be able to use unified metrics. As you know, Google is all about performance and measurability. It turns out DoubleClick has some of the very best tools in the world. We can now use those across the many different services that Google and DoubleClick offer.”

Next: What happens to DoubleClick’s Performics 50 index?