On my HW a fresh UBUNTU 11.04 installation freeze during boot (UBUNTU 10.10 was working like a charm), but only when start from a power down. If you reboot the pc, without power down it, the boot work correctly!
I solve my problem disabling Active-State Power Management.
Edit the file /etc/default/grub inserting pcie_aspm=off as boot option
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash pcie_aspm=off"
Recompile grub.cfg with the command above and restart your PC.
UPDATE: PCI Express is involved on Power Saving regression: http://www.techytalk.info/linux-kernel-2-6-38-2-6-39-power-regression-workaround/