Whenever a web site has chosen a link target on my behalf, it has been wrong; and what's more, "wrong" for me varies by device (e.g. on a desktop computer I don't use tabs and often want full control over spawning windows; whereas on an iPad with a tabbed browser I
usually want tabs created automatically, but not always!).
I think the rule of "least surprise" applies; the least surprising thing for a link to do is to not specify a target at all, leaving the behavior up to the browser (where the browser in turn bows to user preferences and user overrides such as contextual menus). For example, on my iPad I already configure my browser so that different-domain links open in new tabs but same-domain links do not, and I set preferences for a reason: because it's my preferred behavior. These are things the web site couldn't possibly know about me, so the web site basically risks annoying me if they try to override my expectations.
If a web site must feel the need to fiddle with "target" (which I personally think they should not), I think the bare minimum they should do is include an icon or some hint next to non-standard links to indicate what will happen when the links are used. This is another thing that browsers could theoretically do by themselves, since they have all the information about link targets at rendering time.