web 2.0.gifWe talked with people in the hallways of this conference in San Francisco, trying to figure out what single theme trumps all others.

There are all kinds of trends, from the Ajax framework, to RSS, to tagging and more. But what is the uber concept? Our conclusion, perhaps not revolutionary for accomplices of the Internet revolution, boils down to one word: OPEN

It is a familiar, perhaps hackneyed concept. Being open means opening your company’s platform for integration with other services, and for users to be able to communicate back to you, and with other users at other sites.

But it bubbled with relevance yesterday. Yahoo chief executive Terry Semel used the concept of being “more open” to say Yahoo is better than Google. Here is one rough-note version of the conversation Semel had with conference organizer John Battelle:

Battelle: [Google may enter the jobs space] You’ve got hotjobs. From the historic approach that goog takes is scrape and aggregate as opposed to own. Will you give a feed to google?

Semel: We’ll always be more open than they are. [applause from audience] we began with RSS. yahoo in general sees ourselves as an open platform with the ability to publish on yahoo.

Note that search engine expert Danny Sullivan calls Semel on this, giving this example of how Google can be seen as “more open” on shopping and elsewhere. Here’s just a snippet:

If openness is in terms of accepting content, Google deserves more credit here. Google has never played the paid inclusion game, sending out mixed messages of saying they have everything to searchers but to site owners that they’d better pay to make sure they’re included.

Anyway, here is our story in today’s Merc (free registration) on the theme.

We also bumped into Valerie Cunningham, co-founder of GoingOn, who is visiting big companies and trying to help them figure out how to open up their Web platforms, via her company’s offering — which is in the process of being launched. “Some companies say: ‘No, I want to control this stuff,'” she told us. “So we say: ‘Great, we’ll move on to the next one!'”