I agree - the common methods for measuring net promoter (surveys) seem to put a burden on the customers.

I think twitter could potentially be pretty effective if you combine the number of mentions with a sentiment score. But then, it's pretty easy to increase twitter engagement using various tools.

I'm also looking for a good way to measure net promoter, but for another reason -- to quantify it for investors. We hear great customer feedback and get referrals all the time, but don't have a measurement for it. Even though it's true, I'm not sure investors will just believe that "our customers love us!".