A recent article on MSNBC.com titled 'Workers may jump ship as economy improves' articulated several reasons why many employees, and in particular high performing and high potential employees will look to leave their current employer once the economy and jobs market improves. 
Flickr - Sea of Legs
Some of the reasons cited for this conclusion will likely be familiar: lack of trust or feeling that employers care about them, compensation cuts, lack of career development opportunities, and low engagement levels all could conspire against employers seeking to retain their top performers.
So what can an employer do, even today when times are still ridiculously tight, resources are scarce, and everyone feels stressed and overworked (when they are not just thinking about being happy to simply still have a job).
Some of the most important points raised in the MSNBC piece -
'To ensure that employee engagement does not suffer, organizations must rebuild peer networks — especially across teams and departments — to increase employees' connection with their colleagues', and 'Whether an employee's job matches his or her personal interests has the greatest influence on engagement in comparison to all other aspects of the EVP', both have direct implication in the HR Technology space.
Technologies that can help distributed colleagues find each other, surface common interests and skills, and enable some aspects of 'socialization' in the workplace will become more and more important. And workforce planning tools that can be leveraged by both management and employees to help identify and align career aspirations with opportunity can play a major role in determining whether or not some employees choose to move on. A great internal opportunity may be present, but if the right employee does not 'find' it , (or get found), it may as well not exist.
I think in 2010, a major trend in HR Technology will be the development, application, and execution of tools and platforms that will facilitate these connections, help build these networks, and hopefully align worker's interests with the organizational opportunities.