For using her show to denounce Sarah Palin's support of a federal ban on gay marriage.
Ellen has become increasingly political recently and the folks at After Ellen explain her effectiveness:
What makes Ellen's move from famously nonpolitical to outspoken advocate so extraordinary is that she has been able to do it without becoming polarizing. No one brings up Ellen's name when mentioning activist celebrities, nor does she get the derision sometimes heaped on stars like Sean Penn, Tim Robbins and even fellow out comedian Rosie O'Donnell. And I think the reason for this is simple: Ellen has spent all these years on her show being disarmingly likable. And now, quite simply, people trust her.
Hat tip- After Ellen