I know this technically shouldn't be posted here, but I feel that the FS forum users will benefit immensely from the info herein.
As of now, 360 games are to be shipped with the NXE dashboard. Retail games will run perfectly fine, however "backups" with the nxe update will not boot on any present ixtreme console.
The nxe update is placed on a sector of the disk which cannot be read by any 360 running the current (1.5 ix) or previous versions of the xtreme firmware.
This is a security failsafe that was implemented by the creators of the hacked firmware (To prevent live bannings).
There is a new firmware in the works which will be released very soon, but obviously this will only concern those that can flash the consoles themselves.
Just a little warning to those in the market for a flashed 360 looking to play the latest titles.