What would Microsoft do without Steve Ballmer hooting and hollering on stage at its developer conferences? According to prominent hedge fund manager David Einhorn, the company would do a lot better.

In comments made at the Sohn Investor Conference reported by Reuters, Einhorn today called for Ballmer to step down as CEO of Microsoft, reportedly saying Ballmer was “stuck in the past.”

Einhorn is the president of Greenlight Capital, which had $7.8 billion of assets as of Jan. 1.

According to Einhorn, Ballmer is the number one reason his company’s stock has stagnated over the past decade. “His continued presence is the biggest overhang on Microsoft’s stock,” Einhorn said.

While Microsoft’s stock spiked at just under $60 per share in Dec. of 1999, it has since lingered around $25. 

Microsoft’s mobile division has struggled. In early 2008, Windows Mobile controlled just under 14 percent of total smartphone market share, but the company is essentially back to square one, as the iPhone, BlackBerry and Android devices have blown past the software giant in consumer preference.

As of the first quarter of 2011, Microsoft’s total worldwide market share has plunged to just 3.6 percent, according to Gartner.

Many criticize Ballmer for not realizing soon enough that Windows Mobile was dated. The company completely scrapped its “Courier” tablet design to devote all of its available resources in pursuit of a better mobile OS, which eventually became Windows Phone 7.

On the bright side, analysts seemed cautiously optimistic after Microsoft’s latest update to Windows Phone 7 (Mango) was released earlier this week.

To be sure, Microsoft still has a lot of ground to cover if it’s going to catch up to the rest of the pack on the smartphone side of things, but it’s worth noting that Einhorn’s public criticisms of Ballmer are currently among the minority.