Gold members on the xbox will only get access to the free track pack this week (04/01/2011) and then it will be offered to silver users next week.
This is also available for the ps3 as of tomorrow (05/01/2011) on PAL consoles when the store front updates.
No idea if the songs are any good, but certainly worth a download if you have the game. Judging by the title it looks like this could be a series of free downloads.
"Build your Rock Band 3 library by purchasing this song game track pack: Rock Band Free Pack 01. This pack includes "Visions", "Get Clean", "Night Lies", "Shoulder to the Plow", "Neighborhood", "A Jagged Gorgeous Winter", "Conventional Lover", "Supreme Girl", and "Rob the Prez-O-Dent" by various artists. PLEASE NOTE: Rock Band 3 game disc is required to play song game tracks. This song game track pack includes 9 song game tracks at a discounted rate over individual purchases. Many Rock Band 3 songs are available as both a multipack and as a single game track. These songs are exactly the same. It is possible to download the same song twice. For song credits, visit http://www.RockBand.com"
Edit: Thanks for the extra info Ghostbuster.