IT developers don't want to feel like they're getting stale, like they're falling behind their peers. If they're working on a maintenance project rather than a development project, they will find the whiz-bang stuff somewhere else. Another consideration is dollars and cents. I do think how salaries are portrayed by the media is an issue. There are superstars, and I think all IT professionals should look for their value and worth in the market, but I also think there are misconceptions out there.
Quality of life is another retention issue.
They are looking for more leisure time - they want a good salary but they also want to be able to enjoy it. I also think everyone wants to reach a level of self-worth. Each day they go to work they want to know something of value has been added to the project, the company or to themselves. Many of our employees are physically located on a federal government facility with government provided phone systems and computers so our policy is probably a little more restrictive than the average company. Internet and email usage are reserved for official business only.