Microsoft executive Robbie Bach predicts that half of Xbox 360 owners will signup for Xbox Live, even though only 2 million or around 10 percent of current Xbox owners are Live subscribers. However, his comments are not specifically talking about the Gold level membership, which is required to actually take your games online and compete against other players. All owners will have Silver access out of the box, which allows for downloading game trailers and demos. Bach predicts that 50 percent of purchasers will take their console online in some form.
When asked about the possibility for an Xbox 360 MMO, Bach stated that it would be unrealistic to attempt to get an MMO up for console launch, but that "a new MMO" will be available within the next three years.
News source: GamesIndustry.biz