Nothing much specific to this monitor, but mine (manufactured July 2013, bought $200 from newegg in December 2013, rev A00) had some strange dark spots near the bottom that appeared a couple months ago and seemed to be getting slightly worse. It was pretty mild but clearly visible on a uniform background, but only on low brightness settings. Looked kind of like some issue with the backlighting.
Anyway, I got myself a replacement under warranty. Got one shipped here in two days (manufactured May 2015, rev A05), put the old one in the box and off it went. Dell's advanced exchange warranty is pretty nice. No cost, just some hassle of calling around customer support until I ran into someone who could actually deal with the problem. It's relatively difficult without a service tag number for the product (not on monitors 24" and lower) and no original order from Dell, but after harassing enough Indians over the phone, all is well.