At least for the John Edwards presidential campaign:
Second Life has been hit by one of its first instances of political vandalism, with John Edwards's virtual campaign headquarters defaced by apparent supporters of George W. Bush, according to blogger Lyndsay Beyerstein (via Pandagon).
The vandalism included "Bush '08" signs and an altered a photo of Edwards, rendered in blackface (see photo). The vandalists also plastered the area with Marxist-Leninist posters as well as a feces spewing obscenity.
Seems to me that this is a concern for marketers building Second Life outposts as well; it's a bit easier to go to town with vandalism in an online world than in prosaic First Life...