Use it only when you need a new tab/window to open and nowhere else. You don't want to try and make a user's life easier by guessing if they'd open a new tab, because some won't want to. The only place I've used it in months is on Facebook iFrame applications where otherwise avoiding it would cause a larger page to load in a smaller area and get cut off. As another poster mentioned, it would be good to mark as openin…
"The only place I've used it in months is on Facebook iFrame applications where otherwise avoiding it would cause a larger page to load in a smaller area and get cut off."
Which would be the "target" attribute's intended purpose, frames that is.