Employee satisfaction is at an all-time low and a growing number of workers are too apathetic to even head for the exit. How do you get disillusioned workers to change tack?

By Shelley DuBois, writer-reporter

FORTUNE -- Your company is probably carrying dead weight, though it might not be where you think.

Managers often harbor the fear that employees with one foot out the door will lose motivation to work hard at their current jobs, and that's a real problem: more and more people want to leave their jobs today than in years past. Between 2005 and 2010, the number of people who said they were seriously considering leaving their job jumped from 23% to 32%, according to new research from consulting firm Mercer.

"HR departments are very concerned," says Dave Van De Voort, a human resources consultant at Mercer. "As their competitors start to hire, it's going to be very tough to keep people from leaving, and it will be the best people with the best training that will go."

But employees on the way out aren't actually as big of a threat to a healthy corporate culture as the growing ranks of disillusioned and frustrated workers who simply stay put.

Twenty-one percent of the people surveyed in the Mercer study said that they were apathetic about whether they stayed or left. But what's worse is that this part of the employee population had significantly more negative things to say about their companies than both people who were staying and people who planned to leave.

The people within this 21% group are lingering at their jobs for a reason, says Van De Voort, who says that unproductive employees generally fall in one of two categories. The first includes people who are office favorites; they're likeable, but bad at their jobs. Most of those were culled during job cuts throughout the recession. The second type, however, is still around. These are people with a necessary skill. They're valuable, but they're either unproductive or negative influences on others, largely because of the chips on their shoulders.

"You see very highly talented people that have really destructive behaviors, and the organization will tolerate them because they are so talented," says Ken Oehler, a senior vice president at consulting firm Aon Hewitt. More