Timothy Keanini, chief technology officer of nCircle, loves Macs—just not in his company ( a maker of network security and compliance management tools).

Keanini has been both a Mac user and a Mac developer during the past five years. Starting in 2001, he brought Macs into his 100-person company (starting with an Apple G4 notebook for himself) because he believed the user-friendly interface and ability to work in a Unix-like environment would help productivity among the engineering team.

So Keanini, who handled IT decisions until the company grew large enough to bring in a director of IT in 2005, encouraged and officially supported nCircle's approximately 40 engineers using MacBooks.

"The rest of our company was Windows, but engineering was mainly Macs because of me," he says.

But ultimately, instead of productivity gains, dealing with compatibility issues between the Macs used by the engineers and the PCs running Windows used by the line-of-business people in the office slowed down work and resulted in communications issues, he says.

So while Apple's sales continue to grow, Keanini decided to buck the trend, and gave up on his most recent Apple machine, an Intel dual-core based MacBook Pro.

"Between four and six months ago I switched back to Windows," he says. While Apple's installed base is growing, he left the camp he had once espoused to others. He also now advocates that his company's engineers get Windows machines. Even at his home, Apple's role has changed.

"I am all PC at home and at work now, because frankly if I'm not working, I'm gaming. And the Mac doesn't have games," Keanini says, though his household still has three Apple machines in use by other family members.

What makes an Apple loyalist change camps? Here's a look at five reasons why one tech chief did just that.

1. Productivity Trumps Religion

It's easy to fall in love with the aluminum cases used in Mac hardware and the slick interface design of the Mac OS X, Keanini says. Those are two reasons why more people are moving to Apple products: Apple announced shipments of its personal computers grew by 44 percent in the first quarter of 2008, beating the 15 percent growth in PC shipments worldwide, according to market researcher IDC.

Yet, depending on how a company uses Macs, trying to integrate the computers into a company's workflow can kill productivity, Keanini says. The applications never quite match up, data has to be massaged to be useful, and the company has to design workarounds for each issue, he says.