The future of the Web is social. What does that mean? Google is trying to figure it out.

The company's previous attempts to corner the social Web, like Google Wave and Buzz, fizzled or failed to sustain much, well, buzz. But the company is making waves online with a new 216-page slide show that tries to explain how we interact online and how we use those interactions to make purchasing and reading decisions. It's a long, fascinating document, notable more for its clarity of thought than for any mind-blowing insights. So please, consider this a takeaway rather than a digest, and read the whole thing yourself if you're interested.

The Paradox of Online Relationships
We have many different kinds of relationships. Close relationships, like family and best friends. Weaker relationships, like work colleagues. And temporary relationships, like people whose reviews we read on Yelp, or readers who comment on what we publish through Tweets and blogs.

But a social networking site like Twitter and Facebook takes one piece of information from one group and shares it across all groups. This gets people into trouble. Work colleagues see Facebook photos we intend for our friends. Google Buzz revealed private emails to everybody who subscribed to your feed.

It's difficult to design a site that both protects privacy and allows sharing across all these types of relationships. It's almost inevitable that information meant for a small, intimate group gets out to a larger group.

We seek information from a broad network of people, like Yelpers and blog commenters. But we want to share information with a much narrower network of people. A critical challenge for site developers is to design an optimal two-way street that allows us to read and share broadly while locking down our privacy.

What is Influence?
The role of influentials is overstated. We care more about what our friends think than what "important" people think. Gut check: when you go to NYTimes.com, are you more likely to go straight to the op-ed section, or check the "Most Read" list? I know that David Brooks is influential. But I'm pretty sure the Most Read/Most Emailed box is the thing I look at the most. Similarly, I read movie reviews because I like good movie criticism. But I see movies because my friends said they were good.

Influence is tricky. Before we buy or consume or read something, we want advice that we can trust. But what exactly determines trust? I trust Peter Orszag on issues about budget policy, but I don't know if he has good taste in pop music. I trust iTunes' most downloaded list to direct me toward the best new pop singles, but I trust my close friends on book recommendations more than Amazon reviews. In short: sometimes I trust experts, sometimes I trust communities, and sometimes I only trust my friends. Influence is complicated but understanding it is the key to using social media to sell your product or idea.