Yeah, the G2G response time on those Dells is awesome. But, I have been able to detect a slight input lag on my brother's 2405 (and I read that the 2407 is the same). It doesn't bother most people, but if you are really sensitive to that sort of thing, you should try moving a mouse around on a 2405 before purchasing.
Other than that, the 240X monitors are great. I own a Sony Premiere Pro 23" monitor (bought based on THG reviews), and my brother owns a Dell 2405. We are both incredibly happy with our monitors, because we use them for different things. So, it's just a question of what you value most in a monitor.