Getting Ubuntu Linux running on a Lenovo IdeaPad U400
Just wanted to put my experience here as a checkpoint, I know I've found these posts useful in the past for linux hardware. I've installed Ubuntu 12.04 on it and there's nothing which is not working (at least that I've seen). I use the laptop for development (emacs, vms, chrome) and it consistently gets about 4 hours of battery life for me under a real workload and is really solid. I'm using the AwesomeWM Tiling Window Manager, not gnome.
Here are some of the commands that I needed to run to get some of the kinks out. Since I almost never reboot, I just run them on login. The most important one is turning off the dual video, and the xfce power manager, which handles suspending the laptop on lid close.
The only other thing you might need is to check out this bug: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/903853 (search for "padlock" if you're impatient) which helps you resolve low volume of recording. Currently, the work around is to use pavucontrol (Pulse Audio Volume Control) to configure the input channels to reduce extra noise.
UPDATE: If the vgaswitcheroo directory doesn't exist, you might need to remove the fglrx driver: sudo apt-get remove fglrx and reboot.