[plasma]

I think using it is still appropriate when you know the user isn't intending to really leave the page they're on.

For example, clicking on a help link (while filling out a screen) or anything else that would disrupt what the user's doing unintentionally.

[jenniart]

I agree. I think sometimes it's okay when you're sure that the user wouldn't want to browse away from the page they are on... such as when filling out a form or maybe even watching a tutorial video. Otherwise, I think it should be left up to the user.

Personally I tend to use it for links like "follow us on twitter" because I'm hoping that they will keep both tabs open. However the comments here are making me wonder if that's too forceful.

[mooism2]

My expectation when browsing the web is that web apps open external links in new tabs, while mere web pages open links in the same tab. Unhelpfully, the line between "app" and "page" is fuzzy.

[squidsoup]

Agreed - fine for contextual information, help, glossaries, but not to be used indiscriminately.