Quote - As a matter of interest, forcing the user's web browser to open a link in a new page/tab is number 9 on a well-known list of The Ten Worst Mistakes in Web Design.

I can see a point there. Same window is always the safest bet, because than you still have the option to right click and open a new window. If the link automaticly opens a new window you don't have a right click option to force it to open in the same window. Still there are many times where a new window would seem more logical and convenient, e.g. clicking a thumb in a gallery.