In the immortal words of The Clash: "This is a public service announcement... with GUITARS!" Registration is now open for those 20 free tracks offered with the purchase of Rock Band 2.
We're not sure what the free songs will be, but it's probably not going to be The Beatles. Still, though, free is free. All you need to do is visit Rock Band's registration site, enter the info from the back of your manual, and start rocking when the songs are eventually available for download.