Even before Facebook's major revamp last week, a lot of Silicon Valley seems to be declaring Google+ a loser.

A person in the management ranks at LinkedIn (not authorized to speak on the record for the company) told me last week that Google+ rates much lower on the company's concerns list than Twitter and Facebook.

That's despite Google's stated plans to add business features to its social network.

Another executive at a startup that works closely with Facebook and Twitter has been talking to Google about its developer plans for Google+. He likes Google and its developer relations team, but thinks that Google+ is several years too late to have any impact -- unless Google somehow deepens its ties to Android. (He asked not to be named because his conversations with Google were confidential.)

Box.net CEO Aaron Levie said a couple weeks ago that he doesn't think Google+ will get beyond 5% market share.

At Facebook's F8 press conference last Thursday, Google+ didn't come up once.

There's still time. Google+ is only a few months old, and just opened to the general public last week. According to genealogist Paul Allen, who accurately predicted Google+ getting to 10 million users back in July before the company announced it, Google+ sign-ups grew about 30% in two days after it opened up. It's now at more than 40 million users, Allen estimates.

But it's not clear how much those users are doing on Google+, or how often they come back.

So Google is trying to increase engagement by adding games. It just added Zynga's Cityville -- Zynga's most popular Facebook game -- and is expected to open more broadly to game developers in November.

That could help, also.

But meanwhile, Facebook has 800 million active monthly users, who are spending more and more time at the site. It just rolled out its biggest overhaul in three years, with new features like in-line music sharing and a ticker that will encourage people to spend even MORE time on Facebook.

The longer this race goes on, the harder it becomes to see how Google+ can possibly win. Social networking is a zero-sum game. For Google+ to gain users, those users have to spend less time elsewhere. So far, that doesn't seem to be happening.