I have read Jacob Nielson's usability book and he says links should never open in a new window. Here are some of his reasons:
- Novice users cannot manage multiple windows and become disoriented.
- The back button in the new window doesn't take them back to their original window.
- When people want a new window, they'll do it themselves with a keyboard/mouse shortcut.
He says the only exception is links that open in an application, such as Microsoft Word DOC and Adobe PDF. May I propose a new exception? Consider the case when the user is several minutes into a complex web application. There's a link on this application that leads to some advanced help files. So as to not wipe out all of the user's work, that help link opens in a new window. Is this a legitimate exception? Will power users get pissed if the link is forced to open in a new window?