I have a very good reason to use target = "_ blank" in links on my site (please don't tell me about standards). What happens when you click a link on a mobile device? I do not have a phone to check it.
On the iPhone, this will force Safari to open the link in a new tab.
On iOS4 devices, it opens on a new “page” in safari, and the new page focuses. Not yet upgraded to ios5, but I think it is the same, but with tabs. I do not know about other platforms, sorry