I just hooked up a large (30" Dell) monitor over VGA to my ubuntu system (Thinkpad T420 with Intel grpahics running Narwal), and it sort of works, however there's a few things that are very off. On the external monitor only about 3/4 of the space is usable, anything not in that block (which goes from lower-left to middle of the screen) works fine, buy anything outside it is just black, EXCEPT for the top bar, which works, except of course none of the dropdowns can display anything because they go into the black void. On the laptop display things are just generally screwed up, the unity layover is stuck in an awkward half state (not interactive, but still visible) , and no new windows display there. I've also tried using the DisplayPort, however that doesn't work due to a bug in the Narwal kernel I've found.
Edit: http://i.stack.imgur.com/4t1sI.png is a screenshot of what I'm seeing, the only area that is usable is the firefox window.