New window or not?

[pne]

We were talking at work recently about the behaviour of external web links. A co-worker said that he expects that all site-internal web links open in the same window but that all site-external web links open in another window. I expect all links to open in the same window by default, since that gives users a choice: most browsers allow a user to select "open in this window" or "open in a new window". Forcing the link to open in a new window removes one of those choices since both options become equivalent.

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?