The u3011 does have a bit more lag then the zr30w (which I own) but its such a small amount sometimes I think the people who say they notice it are full of ****. Both monitors are a great buy and will be great for gaming, you have to weigh the options I guess? Do you want a scaler(u3011) which is good if your going to play your ps3 on your monitor which im not a fan of and why I have a 40" lcd tv or do you want less input lag(not really noticable), less inputs and a worse return/pixel policy(zr30w) although they did replace 2 monitors for me due to stuck green pixels right near the center of the screen and they didnt have to .
If I had it do over again and the dell was on sale I would get the dell, thats not to say I dont ****ing love my zr30w though as its amazing but the dell is pretty equally amazing + a great return policy if you dont mind talking to Indians who claim to be named Adam if you have a problem.