I have the Dell U3011. I am extremely happy with it. As far as I understand, the U3011 and U2711 use identical panel technology and scaler software and have identical on-screen displays and connectivity options. The only difference is the pixel density and aspect ratio: U2711=2560x1440, U3011=2560x1600. For me, the U3011 doubles as a television screen as well as a workstation monitor, so I needed it to be physically as large as possible but still with high resolution. It's expensive, but I think a high-quality monitor is worth it because it will outlast your computer.
I have my U3011 hooked up by displayport cable (comes with it) to an Apple OEM 5870 (upgrade kit) using a mini-displayport to displayport adapter. Apple doesn't sell this type of adapter but it's the cheapest and highest-fidelity connection possible because the two connectors are electrically the same. I didn't run into the sleep problem; the only issue I've had with the direct displayport connection is that it seems to interfere with the OS X wallpaper-changer, but I was able to find a workaround. Everything also works when booting into Win7 just fine.
I have my previous monitor (which is a Dell 2407WFP-HC) connected by DVI to the same graphics card. Both of my monitors have 100% working pixels and nominally flat backlights. The 2407 has always been a good monitor for me, but the U3011 looks flawless. Make sure you are happy with the anti-glare coating Dell uses on the U3011 and U2711 before you buy, however. I don't think it will match the texture of your ACD.
I have to say that the color fidelity on the U3011 is way superior to the 2407: for example, the U3011 is very consistent across its entire brightness-contrast range, whereas the 2407 takes on a greenish tint at low brightness and a reddish tint at high contrast. I recommend using the "Standard" preset mode and "PC" gamma setting on the U3011 on-screen display, and then using ColorSync to calibrate the monitor.