But while Ace and Simbio successfully migrate small businesses from Windows to Linux servers, Linux on the desktop hasn't been as easy to sell. According to Shank, Linux is currently running on only about 10 percent of all the desktops Ace supports, but a growing number of their clients are running at least some open source software on their Windows desktops.

A major reason Windows desktops are still the rule, not the exception, is that many businesses depend on specialized applications that only run on Windows. For example, right now Ace is in the process of installing 59 Windows thin clients for a medical practice, which has a critical piece of software that only runs with Windows and Internet Explorer.

The client would be happy to run Linux desktops and save license fees, Shank says, "but mostly the app just won't run [on anything other than IE]. It browser-detects and bombs."

Shank says the company that makes it isn't currently interested in supporting anything but IE, so for the moment his client is stuck with Windows even though his servers run Linux.

But many software publishers, from Oracle on down, are starting to provide Linux versions of their products, which means Windows on the desktop is less a necessity each year.

Even without "stealth" sales tactics, Linux is growing in popularity -- and credibility -- among small business owners.

More and more, Shank says, clients specifically ask Ace to switch at least some of their systems to Linux, even if they don't fully understand open source licensing or know how computer operating systems differ from one another.

The reason, says Shank, is that "some people like to brag that they're on the forefront of technology. Basically, they like to brag to their golf partners about it, and they've all seen Linux in IBM ads and think it's cool."