Yahoo eats CEOs. The perennially ailing company lures talented managers into the corner suite of its Silicon Valley headquarters, then it sucks their good reputations out of their veins and casts them aside. They inevitably pass through the revolving door an empty shell of their former selves.
 

Terry Semel, Jerry Yang, Carol Bartz, Scott Thompson. All took the CEO helm with visions of invigorating Yahoo into an Internet leader for the 21st century. Most became mired in Yahoo’s stubbornly byzantine culture. And all probably collected their severance checks wishing to themselves they’d never heard of the company with its stupid hillbilly name and its superfluous punctuation mark.
 

Now it’s Marissa Mayer’s turn. Mayer – an early Google hire who instrumentally forged its successes in search, maps and online email – has become such a positive, likable presence in Silicon Valley that I actually felt sorry for her when I heard it was her time to be Yahoo’s help. A failed tenure as Yahoo’s CEO couldn’t happen to a better-qualified candidate.
 

Mayer’s appointment was something of a bombshell – many people expected Yahoo would appoint Ross Levinsohn, a seasoned ex-News Corp executive, as CEO. In the Internet industry of 2012, the gambit boils down to advertising versus engineering – which is to say, vision versus monetization. Any good Web company wants the sweet spot that welcomes both. With Levinsohn, Yahoo would have got an ad guy to oversee a product that is largely computer code. With Mayer, Yahoo gets an engineer with executive experience.
 

Three years ago, Mayer signaled that she was ready for a new company. Mayer, famously, was responsible early on for the invitingly spartan homepage of Google.com. Later she had a hand in core features like Gmail, Google News and Image Search. During her five years as vice-president for Google’s search and user experience, she oversaw some of the company’s biggest projects, balancing the site’s intuitive interface with the need to generate more ad revenue from it.
 

In recent years, her trajectory seemed to lose energy. Nearly two years ago, Mayer made a move seen by some as a demotion. She was sidelined from search into local initiatives. At the time, local was key to Google’s push into the mobile web, but it also became an area where Google lost ground to Facebook, Groupon, Yelp and others.
 

Remember Google Local? How about Hotpot? Did you love location-based features like Latitude? No? Maybe it’s because nobody else did. Under Mayer’s hand, Google never cracked the local web. Last year, CEO Larry Page pushed hard into social media with Google+, an initiative that seemed to sideline local. And now Google Maps is losing its default place on new iPhones.
 

A year ago, Mayer was bypassed when Jeff Huber was named senior vice-president for local business, previously Mayer’s turf. Again, observers wondered why Mayer wasn’t chosen.

Despite being a public face of the company, Mayer wasn’t counted among the company’s top executives on the company’s corporate page, even before her departure was announced.
 

One can read into this recent history that Mayer lacks the chops to be a CEO, that she’s just bolting to maintain her reputation. Or one could look at her 13 years at Google and see she’s exactly what Yahoo needs. Both of these views are being voiced – but the people who worked alongside her at Google are her loudest supporters. They say she’s smart, hardworking and capable.
 

There is no shortage of voices among former co-workers and colleagues who believe Mayer has it in her to be a capable, if prickly, CEO. Many believe she is just what Yahoo needs. But as welcome as a Yahoo revival would be – and the tepid earnings results Yahoo posted Tuesday show how far it needs to go – the odds of it happening are simply against it, regardless of who is in charge.
 

Corporate turnarounds are painful, ungainly and notoriously difficult things to pull off. When they work, they take years and they usually happen in older, commodified industries. On the Web, things change so quickly and competition is so intense that Yahoo can’t afford a few years to right itself. Other Web companies, like MySpace and AOL have repeatedly tried to turn things around with no luck.
 

And there is a lot at Yahoo to turn around. The company has never had a coherent business strategy. It could never decide whether it was a media company or a technology company. In the glory days of 10 or 15 years ago, Yahoo thrived almost by sheer luck, setting up features like mail, news and financial data that resonated with the Web’s early audience. But that piecemeal strategy endures today to Yahoo’s harm. Google’s mission is to organize information. Facebook’s is to connect people. And Yahoo? It’s a site collecting a bunch of aging Web features.
 

If Mayer can bring Yahoo a distinct and appealing mission, she’ll face other daunting tasks: remaking a corporate culture that smothers promising sites like Flickr into oblivion; building a search asset that doesn’t rely on Microsoft’s Bing; and above all, giving Yahoo a strong presence on mobile devices. If Facebook is struggling on this front, what chance does Yahoo have?
 

All of this will need to happen in a year or two, because by then the rules of what works on the Web will be rewritten all over again. Mayer can buy innovative startups to put Yahoo back on the cutting edge, but it may mean entering bidding wars with Google and Facebook. Yahoo has $2 billion in cash, while Facebook has around $20 billion, Google $50 billion and Microsoft $60 billion.
 

And Mayer will also need to contend with a vocal activist investor on its board, one insisting on profit growth. Web giants like Facebook and Google grow by being willing to invest in risky projects, but Mayer’s hands may be tied by the board’s insistence on short-term growth.
 

Mayer has a lot to bring Yahoo. Her reputation will likely inject Yahoo with a new vigor, stem the exodus of Yahoo engineers and help the company hire new talent. But there will be challenges, too. Her experience at Google search may not be much help at a company that gave up its search engine. Her experience at Google Local doesn’t show a track record of success on the mobile web. And as Mathew Ingram pointed out, Yahoo has become much more of a media company than a technology company in the past few years.
 

A Google veteran like Mayer could have easily raised capital to found a promising startup. Or she could have jumped to a higher title at a Google rival. But signing up as CEO of Yahoo? A company with a fraction of the cash that Google has? Either Mayer has some plan to save Yahoo nobody has thought of, or… well, welcome to the maw, Marissa Mayer.
 

*CORRECTION: Due to a technical error, the piece originally incorrectly referred to Yahoo’s “superfluous question mark.” It is an exclamation mark.