What Do You Think This Endorsement Would Do?

http://www.cnn.com/video/#/video/politics/2008/02/08/intv.powell.undecided.cnn?iref=videosearch

This is video of Colin Powell talking to Wolf Blitzer a couple of days ago about who he will endorse. Powell hasn't made a decision yet, but it sounds like he'd be willing to endorse a non-Republican in this race...

So, what effect would Powell's endorsement of Obama or Clinton have, if any? What effect in general does having someone like Powell cross party lines to endorse a candidate have on a race?