Of course, Yahoo's uptick is largely a product of its re-org and its Panama launch -- both signs that business is getting back to where it should be, and not an indication that Yahoo will crush Google. Google's stock dip, meanwhile, might just be Google coming back to earth after being slightly overvalued. Neither Google nor Yahoo's change in stock price needs to signify a revolution.

But even so, I do see a revolution in the works. It seems that Web 2.0 favors media companies, and can wreak havoc on search-focused ones. That's good news for Yahoo, but spells real challenges ahead for Google.

To see what I'm talking about, look to Google/YouTube.

In the summer before Google bought YouTube, Google Video trailed as the eighth-most popular source for video online, according to comScore. MySpace, Yahoo, and YouTube took the top three slots. As many industry experts have it, Google bought YouTube to buy into a video market it couldn't crack.

As a search company, Google, not surprisingly, was facing a popularity problem in online video. Search destinations are places where you find what you're looking for, and then jump off into content that lives elsewhere. Search engines provide a wealth of navigational information, but they provide little in the way of the richer experience you'd associate with video.

Which is why, when they're seeking video, video consumers would not tend to associate video with search engines. They'll associate video with sites that already do provide other kinds of rich experience -- sites that are rich in their own content, like MySpace, YouTube, or Yahoo.

To overcome that content barrier, Google bought YouTube. But buying its way into video created an entirely new problem for Google as a search engine. If video is a richer experience than most online content, then video search needs to convey more than just raw information about what a video will contain. It needs to convey the whole experience that a video offers. It needs to bring searchers to the video itself.

Which is why video clips live within video search results, in a way Web pages tend not to live within text-search results. That, though, is a copyright nightmare waiting to happen, as there's little to distinguish directing searchers to a clip, and grabbing the clip and hosting it yourself.

We got the first glimpses of that problem last year, when adult publisher Perfect 10, which brought a suit against Google claiming that, in presenting thumbnails of Perfect 10's pictures within Google Image Search, Google was stealing Perfect 10's content. A federal judge agreed.

Newspapers' complaints against Google News, and a pending lawsuit against Google Book Search, are further examples. Google argues that they're providing their searchers with information; the newspaper and book publishers claim that Google is stealing copyrighted content.

YouTube's additional problem of user-generated piracy is an extra twist to the story, but it's still a variation on the same theme. YouTube's piracy problems, after all, only exist because it's so easy to search for any kind of material -- pirated material included -- within YouTube. By providing the capability to easily search for copyrighted material, YouTube --which is to say, Google -- makes YouTube a more effective hosting service for pirated content, even if it conducts that hosting against its will. That opens Google up to copyright complaints.

And so search engines find themselves stuck between a rock and a hard place in Web 2.0. Media consumers aren't just looking to find material on the Internet any more. They're looking to have a total media experience, and to have that experience within one place. And as that trend grows, the line between search results and hosting will get fuzzier, and the copyright issues will proliferate.

For media sites like Yahoo and MSN, which have large amounts of unique content, these problems are far less serious. First, their unique content creates other avenues of monetization, should copyright issues ever threaten a part of their search business. Second, experience as a publisher makes it easier for them-both because of technical experience and corporate culture-to send searchers away from copyrighted content, and toward the content they own themselves. Pure search engines have neither of these options.

To be sure, an ability to help searchers navigate will only become more valuable as time goes on. Google is the leading provider of that navigation, which is why I predict a very healthy future for Google, for a very long time. But there are undeniable troubles ahead for search-only players. And as search and content leaders, Web 2.0 might provide portals like Yahoo and MSN with advantages that Google doesn't have.

This commentary is insightful. I recommend it to others.