FCall it the itch. Many employees catch it, that desire to find the next great job, discover what new opportunities are out there, search for a more sympathetic manager, and perhaps a raise. But the employees who actually take the plunge are often the top 10% of performers -- the engineers who create products, the marketers who sell them, the creative ones who develop new revenue streams. And you certainly don't want to lose them. A December 2011 survey of 3,000 workers conducted by the employment agency Randstad revealed that 47% of employees plan to test the job market in 2012. Complacent employees often sit tight while the ambitious go-getters primed to move up consider new options. But some companies are taking steps to retain their talent and discover why their most valuable staffers might want to depart before it comes time for an exit interview. Nearly half of the employees surveyed by Randstand expect the job market to brighten in 2012, increasing their chances of finding new opportunities. The fact that many employees plan to seek greener pastures reveals a change in attitude over the last few years, says Peter Cappelli, director of the Wharton Center for Human Resources.