Because both previous games were single-player affairs, some Mass Effect players may never have subscribed to Gold. If you want to try ME3 and don't have Gold, don't worry. Microsoft is granting temporary Gold access when you download the demo, so you second-class Free members will still get to try it out.
BioWare's Chris Priestly announced the news on the company forums. He calls it "limited time Gold access," but doesn't specify exactly how long it will last.
So when can you play the multiplayer demo? First access is roped off to Battlefield 3 players. BioWare promised other methods to get in early, probably referring to yesterday's announcement of Facebook missions. The multiplayer portion of the demo will become widely available on February 17.
It's a generous move from Microsoft; but of course, it probably helped that the series is multiplatform now. PlayStation 3 and PC players will be able to access the multiplayer portion for free, so this helps Microsoft offer parity for a demo in a series that was once Xbox 360-exclusive.
Mass Effect 3 is coming to PC, PlayStation 3, and Xbox 360 on March 6.