My co-worker argued two things: (a) every click is a click too many: people are lazy so make the default action require as little as possible, and (b) the default action should be to open external links in a new window so that they can easily return to the site they just left -- since you want to try to keep them on your site as long as possible.
I'm not sure; after all, in theory "the customer is king" and you're supposed to serve him so the way to keep them on your site is to make the content easily accessible and interesting, not by browser gadgets such as popping up new windows.
What do you think? Should "exit links" open a new window or not? What do Internet users expect from clicking on a link?