On the Internet, 20 months is an eternity – yet that’s how long Yahoo stuck with the most recent design of its front page. In fact, it was enough time for the emergence of an entirely new way of using the Internet, loosely called “Web 2.0” and focused on user-contributed content, media tagging and sharing, social networking, and browser-based services, rather than desktop software.

Catching the Web 2.0 train before it leaves the station is what the just-released redesign of Yahoo’s front page is meant to do. Starting today, visitors to www.yahoo.com/preview* will see a radically different layout, which emphasizes an interactive “Personal Assistant” and links to the most popular content from Yahoo’s large network of sites and services, such as Yahoo Music and the Flickr photo-sharing service.

The redesign is one of most drastic in Yahoo’s 12-year history, and it’s the most visible step yet toward the company’s recently expressed goal of transforming Yahoo from a search portal into a locus for personalized information and community-generated content, ratings, and reviews.

For a year or more, a common buzzword uttered by Yahoo engineers and executives has been “social media” – the idea that one-to-many communication on the Web has given way to many-to-many communication, and that traffic and conversation naturally cluster around content, such as videos, photos, blog posts, and bookmarks. Examples of social media in action at Yahoo include My Web 2.0, where users can save, share, and tag Web pages they’ve visited; Yahoo 360, a free blogging and social networking service; and Flickr, which first popularized the concept of “tagging,” or adding informal labels to content such as photos to facilitate searches later.

Now its front-page redesign puts social media right up front at Yahoo for the first time. It also indicates how the company may go about restructuring its offerings around the knowledge and media that average users upload to the Internet by the gigabyte every day, as well as the collective “wisdom” they demonstrate through their viewing and shopping behavior.

“What you’ll see on the new front page comes from listening to our users about what they do [on the Web],” says Ash Patel, Yahoo’s chief product officer. “It helps people connect with the content and the people that matter to them, either through search or e-mail or community-generated content.”

Web 2.0 makes its most prominent appearance on the new front page in the form of Yahoo Pulse, a space for popular listings and user-contributed media drawn from other Yahoo properties. A lucky photographer who uploads her photo of last night’s glorious San Francisco sunset to Flickr, for example, might wake up the next morning to find that millions of Yahoo users have been served a thumbnail image linking directly to the photo.

* Correction, May 18, 2006: An earlier version of this story stated that beginning Wednesday, all visitors to Yahoo would see the new front page. In fact, it is still necessary to visit Yahoo’s “preview” page at www.yahoo.com/preview to see the new design; once someone has visited that page, it becomes the default Yahoo front page on their computer. Yahoo says that the new page will become the default front page for all visitors over the “coming months.” 

“What makes the Internet great is all the people who are on it,” says Patel. Pulse – an improvement on an earlier feature called Yahoo Buzz – also links to most-watched videos, most-downloaded songs, most-purchased apparel, and the like. It “shows the things that users are clicking on and rating and using and buying,” Patel says.

Another front in Yahoo’s social media invasion is Yahoo Answers, which finished its beta-testing phase and became an official Yahoo product on Monday. The service – accessible via a link directly underneath the search box on the new front page – allows people to enter plain-language queries and get replies from other users, who are then rated according to the quality of their answers. Call it a human search engine: it’s a way for someone seeking the best way to get rid of a dog’s fleas, for example, gleaning advice directly from other dog owners, rather than sifting through pages and pages of search results and advertisements for flea powder.

For sheer technical coolness, though, the leading feature on the new front page is Personal Assistant, a panel with six buttons, labeled Mail, Messenger, Radio, Weather, Local, and Movies. Scrolling a mouse pointer over one of the buttons causes the box to expand, showing details such as the user’s latest e-mail messages, a list of his or her Yahoo Messenger buddies who are currently online, local weather reports, and maps showing traffic congestion on local highways.

The Personal Assistant’s animated, interactive behavior means that users can obtain information specific to their needs without having to click away to a Yahoo subsite, such as Yahoo Mail or Yahoo News. It operates on programs written directly into the page’s source code using the AJAX programming approach, which typically works well in some browsers, such as Mozilla Firefox, and less well in others, such as Internet Explorer. But Patel says Yahoo engineers worked overtime to make sure that the Personal Assistant would function correctly in all common Web browsers. “This is probably the most extensive use of AJAX for such a large audience of any page on the Web,” Patel says.

In fact, Yahoo.com is the most trafficked property on the Web, with some 180 million unique users every year – 345 million, counting the company’s properties in 24 other countries. But the percentage of actual Web searches conducted using Yahoo has dropped of late, with Google picking up the slack. What’s more, Google now offers its own services such as e-mail, an online calendar, local maps, photo-organizing software, and a personalized search page.

Yet in almost every one of these categories, Yahoo’s services are still more popular than Google’s. Yahoo’s challenge has been creating a unified user-centric packaging for its at times unclear “core identity” and its complex, poorly integrated set of offerings.

Yahoo’s redesign is an attempt to smooth access to its services, and could well help to pull users back from other personalizable sites, such as Google and Microsoft’s new Live.com. It’s a sortie in Yahoo’s Web 2.0 offensive, and – with investors watching closely – it’s a battle the company can’t afford to lose.