Installation of 12.1 is a bit more complicated as previous versions, now i need to supply acpi=off kernel boot arg to normally start, otherwise system hangs with garbled screen like with wrong resolution after 'starting udev' string on 'loading basic drivers'. Don't know yet what is the reason and is where any normal fixes, turning off acpi works fine for now.
Update1: Found also that 12.1 on XPS M1730 wont clearly shutdown, same way as mac os x do. Tried to switch from systemd init to good old systemv(F5 at grub boot screen), no diffirence. /usr/share/kde4/config/kdm/kdmrc tuning of HaltCmd to '/sbin/shutdown -h -P now' didnt help also. Acpi is only thing left 8) Time to patch dsdt.aml
Update2: Fixed very easy, acpi=off persist in grub menu.lst after installation, removing it, made system shutdown fine.
