Microsoft has released the promised DRM Transfer Tool for consolidating Xbox 360 content licences. This sort of thing is why we became gamers in the first place.
As you will know if you've upgraded from a Core or Premium model to an Elite, or if for some other mysterious reason you've had to switch your profile to a new system, playing licensed content like Xbox Live Arcade games on your new machine requires you to be connected to the Internet. The DRM tool stops you having to do that.
The tool can be used once a year and is accessed through www.xbox.com/en-US/drm. Microsoft says it only takes one minute to do, and there's a video of Major Nelson showing it off for those of you who need assistance.
The main caveats are that movie licences are non-transferrable ("Movies are not 'download-to-own' so the licences are not transferrable," says Gamerscoreblog), and if you have to send your Xbox 360 to Microsoft for repair any time soon they will automatically update its licences for you.