In order to be used at its higher resolution ranges, the refresh rate has to be at 30hz, which is very hard on the eyes and was giving me a headache. I was forced to reduce it to the recommended, mid range resolution (with a refresh rate of 60Hz), which is nothing remarkable, making it just an expensive ordinary, albeit large, monitor. Colours are also not great. I use a Spyder 3 colour calibration tool and three separate monitors on the same system (including this one), and while I can get the other two to match exactly, the Dell is always too purple. It's not bad by any means, but side by side with my Wacom Cintique and an older Dell, it isn't great.
Overall, it's not bad, and it's the cheapest 4K monitor around, but I wouldn't recommend it as it falls short of its promise.