Look for the U2713 to start shipping in about a month.
The U2713 will have a new panel type.... the AH - IPS. It's really just a more energy efficient panel. If you are an energy efficiency aficionado, then this is the flat panel for you, otherwise, you might be just as well off with the U2711.
On paper I don't see a lot of differences... the U2711 actually has a faster response time and apparently a wider color gamut... but I haven't tested both side by side so I can't really say which looks better in the real world.
Aesthetically I do like the U2711's squared off corners instead of the rounded edges, but that's just me.
Either way, you can't really go wrong. Me personally, I'd take the deal on the U2711.