The New York Times campaign blog has an interview with the designer of the Obama logo. I was interested in the designer's initial discomfort with alterations of the logo--it seemed very old-school brand ideology; he wanted total consistency and control. But alteration worked very well for the campaign (this link shows lots of intriguing logo variants adopted for subsegments of Obama's supporters), and it also allowed people to take ownership of and express their support for the campaign. My husband made me a Yes We Carve pumpkin for Halloween (see also Republicans for Obama logo). Then there were, among others, Craft for Change, Obama pies, cookies, and the handmade paper plate logos I saw at my local volunteer station. These all strengthened the Obama campaign, regardless of what traditional trademark ideology would say.
The lesson: the trademark owner should probably think of itself as a brand manager, not an owner.