Thurrott speculates that Longhorn will include a subscription feature for automatic virus updates, and complains that the anti-virus feature should be free as are features like the Windows Media Player, etc.. It seems that Microsoft is trying to preserve the market for third party anti-virus software providers (maybe they're concerned about even more anti-trust/anti-competitive claims?).
I'm not sure where I stand on this one. Once Scoble is able to start talking more (PDC timeframe?), maybe he'll weigh in on this one.