ive recentley softmodded my second xbox using the blackwars installer, No need to uninstall the mod to get onto live - works fine when you cold boot the system.
(by cold boot i mean load an original game in the tray and reboot your xbox - when started with an original game the softmod does not start).
Ive been using this method for a week now with no problems - but its strictly a 'use at your own risk' way of doing things.