I’ve not been as opposed to opening new windows as Jakob Nielsen. If you have a site that is populated overwhelmingly by expert users then there are many very good reasons to open new browser windows and little-to-no downside.
To the extent that Nielsen is talking about ads or gratuitous using of “new technology” for its own sake I agree with him. There are also some sites which open new windows for every link - these are not professionally developed sites and for that reason I don’t consider them as part of this discussion.
To the extent that you have a site that is populated with average users I agree with him. One of Nielsen’s missions is to constantly remind computer professionals – developers, designers (as well as Usability Professionals) that the average user gets lost a lot more often than we do AND gets confused, bewildered and frustrated when lost. And that’s important, angry frustrated customers don’t come back; confused and bewildered staff waste time and are resentful that they’re forced to figure something out.
Still the mantra that one should NEVER create new windows is, I predict, soon going to be obsolete. Now that IE 7 has come out with tabbed browsing it will soon become part of virtually every web user’s repertoire.
The questions that will then need to be answered over the next few years is: how many people take advantage of the tabs? And does the use of tabs make opening new windows more acceptable, as predicted above, or does the average user continue to be thrown by use of opening new browser windows?