(Corrects share buyback price in seventh paragraph and Apple stock ownership in last paragraph.)

Nov. 6 (Bloomberg) -- Dan Loeb, the billionaire founder and principal owner of Third Point LLC, the $14 billion activist hedge fund, has made about $1 billion for himself and his investors from a two-year crusade to increase Yahoo! Inc.’s stock price. He’s been extraordinarily successful; the shares trade for about $33 these days, up from about $13.50 when Loeb started buying them in September 2011.

But while Loeb was busy cashing in, what benefit did Yahoo’s 627 million unique monthly visitors (me among them) get from his 26 months (and counting) of ownership?

The answer: not much, except for some major new headaches. This raises the legitimate concern that the saber-rattling by certain activist hedge-fund managers is designed to benefit them, not the companies they target or their customers.

In his typically aggressive fashion, Loeb indeed rattled every possible Yahoo cage. He criticized the board for hiring Carol Bartz as chief executive officer. He said the board made a gross error by turning down Microsoft Corp.’s $31-a-share offer for Yahoo in 2008. (The stock was trading at $13.61 at the time.)

He accused Yahoo founder Jerry Yang and board chairman Roy Bostock of “strategic bungling.” He described Bostock as “a lame duck outgoing Chairman.” Loeb famously uncovered the “discrepancies” in the education record of new Yahoo CEO Scott Thompson, who had claimed his degree from Stonehill College, outside Boston, was in accounting and computer science when it was just in accounting. “Now more than ever Yahoo! investors need a trustworthy CEO,” Loeb wrote in May 2012.

CEO’s Resignation

He called for Thompson’s dismissal; 11 days later, Thompson resigned. Loeb then joined the board, as did his two designees, Harry Wilson, an investment banker, and Michael Wolf, a media consultant. In July 2012, Loeb recruited high-profile Google Inc. executive Marissa Mayer to lead Yahoo. According to company filings, the Yahoo board offered her a pay package of $60 million, including future bonuses and other compensation, to make up for what she lost by leaving Google.

Loeb’s payoff for all this hard work came a year later, when the company announced an unusual arrangement: It would buy two-thirds of Loeb’s 60 million shares at the market price of $29.11 per share, for a total of $1.2 billion. He still owns 20.6 million Yahoo shares -- worth about $700 million -- and remains the company’s sixth-largest shareholder, although neither he nor any of his designees is still on the board.

While Loeb and Mayer have done well, Yahoo’s users, especially the estimated 275 million Yahoo Mail users, have suffered mightily. Last month, Mayer announced a revamp of the Yahoo Mail user interface. Many people think, not coincidentally, that it looks like a clone of Google Inc.’s Gmail.

According to the New York Times, there have been tens of thousands of user complaints: everything from “The new Yahoo is so bad it’s tragic” to “IF IT AIN’T BROKEN DON’T FIX IT” and “It just feels like Yahoo doesn’t care about users like me: Longtime, loyal, paying customers who were happily using the Yahoo service.”

A Yahoo forum contained additional complaints, such as “new page layout sucks! Have to scroll through two screens to find send button. Hate it” to “left navigation column does not show photo folder any longer. Bam...gone. just like that. Who knows where all my photos went? Please don’t tell me they are all stuck within all of the thousands of email message now.”

My own recent experience with Yahoo Mail is just as frustrating. Beginning about two weeks ago, my premium Yahoo Mail -- I pay for extra storage -- would no longer load my e-mails. The redesigned template appeared, but instead of my e-mails, I received a succession of technical-error messages telling me the problem was only temporary and would soon be resolved, “usually within minutes.”

E-Mail Problems

This went on for about 10 days, making it virtually impossible for me to communicate by e-mail. Who knows what commercial opportunities I lost as a result? I wrote Mayer an e-mail from a different account -- my Apple iCloud e-mail -- informing her of my ongoing problem and seeking her help. I never heard back. (An unrealistic expectation, you say? Well, she did respond -- in the negative -- to my request for an interview when I profiled Dan Loeb in Vanity Fair recently.)

Twice, I managed to speak to a live person in customer service, which is a major accomplishment because Yahoo is notorious for making it difficult for customers to reach a human being. (Yahoo prefers to receive complaints through a customer-service e-mail template.) Anyway, one of the Yahoo representatives I spoke to told me the problem was with my Apple computer, not with Yahoo, and that I should try to access my Yahoo e-mails from a PC, not a Mac. (I tried; no luck.)

My personal computer guru, Eliot Burkett, e-mailed me at my Apple account that “none of this has anything to do with the problem. The issue is totally on their end.”

Although quite friendly, the other Yahoo representative told me he couldn’t help me but said customer service would send me an e-mail. You guessed it: It was another of those useless e-mails that go nowhere and fix nothing.

At the moment, my Yahoo Mail is still blinkered. Occasionally, my e-mails will load into the template, but individual e-mails do not open, except on the rare occasion, and they can’t be deleted or responded to. I am at least able to see who e-mailed me to ask them to reach me through my new Apple account. That has been a saving grace. At the moment, my Yahoo Mail tells me -- incorrectly -- that I have more than 170,000 unread e-mails.

In the “even paranoids have enemies” category, I note with interest that my Yahoo Mail trouble began just as my recent (and critical) profile of Loeb was about to hit the newsstands. It seems highly unlikely that Loeb would call up Mayer, or otherwise arrange, to sabotage my Yahoo Mail account. After all, other users have had problems, too. For instance, on Oct. 30, user Todd Gordon wrote: “Yahoo mail sucks. Not working AGAIN! You mess with the codes and this is what happens, millions of pissed off campers. FIX IT!”

On the other hand, my Yahoo Mail really doesn’t work anymore and there appears to be no prospect of a near-term fix, just an interminable stream of temporary error messages.

So as of this moment, loyal readers, please note that my new e-mail address is wdcohan@me.com, a part of the Apple universe. I really hope this works, although I note with concern that Loeb’s activist hedge-fund buddies Carl Icahn and David Einhorn sure own an awful lot of Apple stock.

(William D. Cohan, the author of “Money and Power: How Goldman Sachs Came to Rule the World,” is a Bloomberg View columnist. He was formerly an investment banker at Lazard Freres & Co., Merrill Lynch and JPMorgan Chase.)

To contact the writer of this article: William D. Cohan at wdcohan@me.com.

To contact the editor responsible for this article: Paula Dwyer at pdwyer11@bloomberg.net.