I have never been sure whether it is best to have external links open in a new window, so that the reader is not leaving my site when he clicks on one of my links to other sites.
Up to now I have mostly had the links open in the same window, following the recommendations of Dr Jakob Nielsen. He has always said that that is what the reader expects, and that the reader gets confused if more than one browser window opens.
But I still fret that I am losing my readers as soon as they click on the first link they fancy on one of my pages of external links. I know that where the default is set to open in the same window, experienced users can easily force a new window if they want one, e.g. by pressing CTRL while clicking on the link. But do many users actually bother to do this?
Also, is there anything to be said for having internal links open in the same window, but external ones in a new window?