What's Yahoo! (NASDAQ:YHOO) worth? With every passing tick, the market gives us its perception of the search giant's value. But what if the market is wrong?

That's the thesis proposed by analysts at Sanford C. Bernstein this morning, suggesting that the sum of Yahoo!'s parts is worth roughly $39 a share. The analysts argue that the company could ultimately be worth as much as $45 a share, in the hands of a buyer savvy enough to unlock that value by making the necessary incisions and decisions.

That latter figure would be a 66% premium to yesterday's closing price for Yahoo!, but don't assume that Bernstein knows anyone who'd actually pay that much for the company in its present state.

Five times the love
Yahoo! has been a classic underachiever in recent years. Its collection of websites generates more traffic than rival Google (NASDAQ:GOOG), yet the market graces Google with a market cap five times greater than Yahoo!'s -- for good reason.

Most of Google's traffic comes from search-engine queries, which are clearly a lot easier to monetize than Yahoo!'s various sticky sites for free email or photo-sharing. Folks go to Google because they want to go somewhere else, and Big G is there to collect money from sponsors for the click-through referrals. Google's chunky Rolodex of advertisers has also made it a top choice for third-party publishers, who let Google broadcast their contextual-marketing ads in exchange for a piece of the action.

It all boils down to prettier income statements for Google. The company generates twice as much revenue as Yahoo!, and it does so with substantially wider profit margins. Even though Yahoo! is valued at one-fifth of Google, it's actually generating even less than one-fifth of Google's profits. Can you believe it? Yahoo! seems to be the overvalued one here.

But wait just a second. Remember that roughly a third of Yahoo!'s market cap is spoken for by stakes in Yahoo! Japan, China's AliBaba, and Korea's Gmarket (NASDAQ:GMKT). The rest of Yahoo! may still seem pricey, given the company's meandering ways, but let's not assume that a private-equity firm is the only one willing to make some gutsy calls and carve Yahoo! into something exciting.

After all, one of the more tantalizing calls for unlocking the value at Yahoo! came from inside the house. President Sue Decker called Yahoo! Mail "a dormant social network" during the company's second quarter conference call this summer.

That's a golden opportunity, even for a company that seems destined to settle for silver medals on the search-engine front. Yahoo! Mail has 250 million active accounts. A ton of those users check their inboxes several times a day. All of that friction can't be a bad thing, especially if Yahoo! uses that as a platform to further engage its email browsing audience. The company has beefed up some of the features of its mail website, but there's room for greater improvement.

A 100-to-Yang long shot
Shortly after Jerry Yang was installed as CEO earlier this year, the Yahoo! co-founder mentioned that he would take 100 days to take a sobering look at all of his company's moving parts. For those following the clock at home, those 100 days will be up later this month.

So even if the Bernstein analysts are overly optimistic, or simply rushing to judgment, Yahoo! is still sensing shareholders' growing urgency. It's there. It's thick. It's deceptive.

See, anyone can point to the stars in Yahoo!'s portfolio, such as Flickr and Yahoo! Answers. But a lot of people aren't writing about the cool things that have been happening at Yahoo! since Yang took over. The company's made timely acquisitions, including those email enhancer and Web-apps enabler Zimbra, and has launched new products such as Yahoo!'s Mash social network.

So what if Yahoo! doesn't become a Salesforce.com (NYSE:CRM) in Web-based software, or a rival to News Corp.'s (NYSE:NWS) MySpace in social networking? In its quest to unlock value, Yahoo! has a whole ring of keys to try out.

Last month, I suggested that Yang -- or as I called him, The Great Yangini -- is transforming the company into something worth owning, even though everyone assumes that the company is in limbo until Yang's introspective analysis is complete.

So what's the rush to undo Yahoo!? By the time it's all over, the Yahoo! you see may not be the same Yahoo! you thought that you wanted to undo in the first place.

Things that Yahoo! did during its summer vacation:

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.