Sometimes these are genuinely new products that do the job better or differently (Method: cleaning without toxic chemicals), sometimes they are designed to address a social-economic or environmental problem (The Tap Project), but often they are just a restatement of the product's basic benefit in advocacy terms (e.g., Wisk's "Go ahead. Get dirty").
Dove's Campaign for Real Beauty had an enormous impact on refreshing the brands relatively tired image without advocating for something specific to change about the world. While some of the work contained critiques of the fashion industry's unrealistic standards of beauty, the majority of its communications focused on a positive celebration of the beauty possessed by un-photoshopped real women. No petitions for the fashion industry to change; just how we perceived it. This was political advocacy from the inside out.
While cause-marketing began as a way to use mass marketing as a tool for behavioral change (e.g., Iron Eyes Cody on behalf of Keep America Beautiful), and then became a promotional tool (many experts mark Amex's 1983 Statue of Liberty Restoration Program as a turning point), it's clearly evolved into something even fundamental: a platform for brand strategy. When brands want to have a major impact, they often feel the need to take a position on something bigger than dirty clothes or headaches.
It's easy to see why: in a cluttered marketing landscape, brands need new ways to get attention and differentiate from their competitors. Brand X might clean clothes, but brand Y cleans clothes without poisoning the river, etc.
This isn't to say that the familiar forms of cause marketing aren't still around: there's Crispin's breakthrough Truth work and Droga's Tap Project and endless amounts of promotional tie-ins. But more common these days are brands that take a position simply because it's good for business.
And there is the highly visible RED effort, raising money to fight AIDS in Africa, is both a brand and a cause, which has linked itself to a consortium of brands and promotions. It's almost a holding-company brand for cause-marketing.
In fact, the field has gotten so diverse, it's probably a mistake to call all these programs cause marketing at all. Various people have suggested alternatives: advocacy brands or passion brands or enthusiast brands, but they all take a position to emphasize their commitment to something consumers care about more than their brands. (Thanks to Gareth for hooking me up with so many insightful perspectives on the subject)
Grant McCracken tends to view all this as a positive development:
"In order to get access to the power and authenticity of the new beauty movement, Dove makes available its marketing cunning and check book. To get access to Dove's cunning and checkbook, the trend makes available its power and authenticity. Intellectuals are found of talking about how capitalism corrupts culture, but this bargain looks like a pretty good one."
I'm inclined to agree, though I wonder about two unintended consequence: 1) the incessant linkage of consumption with positive social change weakening our belief in more direct forms of political action (e.g. voting). You can't improve all the ills of the world by buying stuff and 2) a consumer backlash, something like cause-exhaustion, during which we hunger for brands that don't ask for anything but our money and in return do their intended job. Only time will tell.