This excerpt taken from the AN DEF 14A filed Mar 23, 2009.
In certain cases upon a termination or change in control, the vesting of unvested stock options and shares of restricted stock is accelerated. To determine the value of unvested stock options that would accelerate in such cases, we calculated the difference between (1) the exercise price of the unvested stock options that would accelerate and (2) the closing price per share of our common stock on December 31, 2008, which was $9.88. To determine the market value of unvested shares of restricted stock that would accelerate in such cases, we multiplied (x) the number of unvested shares of restricted stock that would accelerate by (y) $9.88.
As of December 31, 2008, all unvested stock options held by our named executive officers had an exercise price higher than $9.88. Accordingly, even though in certain cases unvested stock options held by our named executive officers would accelerate as discussed below, no value is attributed to such acceleration. Since vested stock options are already exercisable upon termination (except in the case of a termination for cause), no value is attributable in the tables to the extension of the exercise period for such vested options.