When the Mass Effect 3 demo launches on February 14th, Silver members will be able to log right on and enjoy the game’s online component. I’m not sure how much time you’ll get to enjoy the game’s multiplayer but judging from this exert by Microsoft, it looks like you’ll be able to play all the way up to the game’s March 6th release.
Battlefield 3 online pass activators will enjoy the game’s multiplayer outright though. It’s a cool gesture I guess and nope I don’t know if you’ll be able to utilize that online access with other games.
“In celebration of ME3, Xbox is pleased to provide fans access to ME3 demo multiplayer for the time leading to launch. Xbox LIVE Gold gives you exclusive benefits including multiplayer gaming, member-only deals & previews, and access to entertainment with Netflix, ESPN, Hulu Plus and more.”