Sure enough there is not only a fourth Bourne novel but a fifth as well -- both written by thriller veteran Eric Van Lustbader (I've read his The Ninja -- it moves along with conviction [and according to Lustbader's website is being adapted for the screen by 20th Century Fox with a script due in months]). The next Bourne movie, should there be one, is The Bourne Legacy. The fifth novel, not yet finished, has a working title of The Bourne Trajectory (that will have to be changed for a movie, sorry).
As long as they can keep the quality of the material top-notch, I'm all for more Bourne stories. Bond may have been the thing way back when, but he's a bit superficial (as well a sexist in a backwards way) today -- Bourne has much broader appeal and audiences connect with Damon. Rock on Jason (and hope you work out that memory thing).