Ubuntu upgrade to 12.04: screen only works with 1024x768

After upgrading a laptop-system to 12.04 (precise pangolin) X only starts with a resolution of 1024x768 and not with 1366x768.
I followed many postings and tried many things:

• add new resolution with xrandr (here)
• create a xorg.conf file (here)
• add new drivers (here)
• ...

But there was only one thing wrong: /etc/default/grub

After changing the following line everything worked:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash i915.modeset=0

to

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

(i added i915.modeset=0  because with the older ubuntu version hibernate does not work and this configuration fixed it. [link])