Twitter can be good. It's great for newsfeedy type stuff. It's awful for discussions or shouting at clouds.
I think as a site, twitter could be useful for getting retweet action from other u2 news sites (obviously 'rival' forums wouldn't promote it) to raise awareness of this forum's existence.
As this isn't a news site, the reach and purpose of Twitter isn't as useful as it is to say @u2 or @u2fanz