Well it looks like the rumours on this one were true, MS have just released a new tool that will let you transfer the licenses for all your downloaded content from one console to another. So if you fell victim to the RROD or had to get a new console for some other reason, then this is definitely something you need to check out.
For those who don't know, DRM (digital right management) is a way of locking your downloaded content to the console and gamertag that you downloaded it with. So this means that anyone who signs on to the console it was downloaded to can use it, or the gamertag that downloaded it can use it on any console, as long as they are signed in to Xbox Live. This meant that if you got a new console, only your gamertag could use the arcade games etc. that you downloaded (any other profiles on the console would just see the trial versions) and you had to be signed in to do it.
Now with the help of this tool, you can transfer the licenses to your new console. There are a couple of catches - the main one is that you can only do it once every 12 months. Also you can't transfer licenses for movie rentals (not that we have the video marketplace here in Australia, so I don'e care about that one). And lastly (and this is an important one if you are outside the US) to get to the tool on xbox.com if you are not in the US, go to https://live.xbox.com/signup/UIPStartPage.aspx?appid=ConsoleLicenseTransfer instead of www.xbox.com/drm, otherwise you will get a page not found error (Found this fix in the comments about the tool on Major Nelsons blog, Litheon posted it).
For more information, check out the FAQ on Xbox.com (use the link above) or Major Nelson's blog.