I'm using a Dell U2312HM monitor with my Lenovo X220 (Intel HD 3000 graphics card) via DisplayPort at work. Sadly, there is an issue with this combination: The Dell flickers once in a while. It's only a short flicker but working with the Combo for 8 hours (I'm a programmer) still makes it annoying. There is no "rythm" to it, it just randomly flickers. Sometimes 5 minutes between the flickers, sometimes it's 20 or more.
Switching the VGA driver for newer or older ones didn't help. Switching to VGA cable helps but the picture is not as fine as the DP one, that's why I want to use it.