In this month's issue of Fortune, we "meet the most important young iconoclasts, risk-takers, and rule breakers in business"—40 of them, to be exact. At the top of the 40 Under 40 prestige pile is Yahoo! CEO Marissa Mayer, who, despite lavish press, has accomplished about as much for Yahoo! as you have.

Here is why Mayer rests—and I do mean rests!—atop the list, according to Fortune:

"Get in over your head" is Mayer's guideline. It's this career philosophy that has fueled her turnaround effort at Yahoo since she joined the company as CEO last year, at age 37, after more than a decade at Google. Mayer has replaced key Yahoo executives, made a string of acquisitions (22 so far, including Tumblr—see No. 24—for $1.1 billion), and overhauled Yahoo's culture and HR rules (its logo too) in an effort to make the company innovative again. Revenue growth is her challenge, but investors like what our newly crowned No. 1 has done: The stock is up 86% since she came in.

This is all more or less true, but by no means justifies a top spot, to say nothing of "iconoclast." Examine any of these sentences alone, and you'll see a corporate black eye, not plaudits.

But fine, this is Fortune, not an epic poem, and so it's enough to be a above-capable businessperson. Is she?

Mayer landed at Yahoo! after a series of clear demotions at Google—she entered the former after a downward slide at the latter. Over the past year and change as CEO, she's earned headlines and retweets not through her deeds, but through discussion of her deeds. Corporate theater, innovation as exhibition—Mayer is a household name (at least in geekier households) by virtue of being Marissa Mayer. She's gotten people talking about Yahoo! into conversations again, but can any of us remember what any of those conversations were about? Repeating a noun for its own sake doesn't do much to elevate that noun, no matter what purple font it's rendered in.

Push aside URLs and magazine spreads, and what's left? What has Marissa Mayer done? How has Yahoo! changed under her?

  • She's pissed off the company by banning people from working from home.
  • Yahoo! Mail received some new features, about a decade after it would have mattered.
  • The company's Yahoo.com homepage saw some minor changes.
  • A bunch of old shit from the 90s that no one used anymore was shut down.
  • Yahoo! bought Tumblr for far less than its investors hoped, largely because Tumblr was going to run out of money soon.
  • It also bought 21 other pissant startups on the cheap, earning attention and little else along the way—some of these TJ Maxx sale rack acquisitions were folded into existing products to bolster apps. None of Yahoo's iOS apps are in the top one hundred most popular free downloads.
  • Flickr saw a big redesign—and a good one!—years after most users had moved on.
  • Mayer sat in a chair, upside-down, for a Vogue September Issue spread.
  • Mayer spent a weekend designing a new logo for the company, which everyone hated.

In summation: bought a bunch of middling companies, bought Tumblr, minor page design changes, a new logo, a magazine spread, and no working from home. The company's stock value has leapt, sure—but this is almost entirely the fruit of a fortuitous investment in Alibaba, a an enormously successful Chinese startup being successful on the other side of the planet without help from Mayer. When the Alibaba cash runs out—and one day it will—which of the aforementioned feats will Mayer be able to lean on? The logo? Giving a teenager $30 million?

Self-perpetuating buzz is a short term enterprise, and Yahoo! under Mayer has been all about the short term.

What can Mayer do that'll get people talking about Yahoo! today?

What can Mayer do that'll get people talking about Mayer today?

How can Yahoo! keep its head above water for one more day? What do we have left? Well, we can always change the logo. AllThingsD's Kara Swisher calls Marissa Mayer the "Hey-look-at-me" CEO. That's not entirely fair: she has places like Fortune saying "Look at her!" just as much. For a peek at real corporate power, it'd be hard to avoid staring at Sheryl Sandberg, disqualified from the Fortune list by her age on a ranking that includes Will.I.Am. Maybe we should just look away from lists entirely.