I have and it's awesome. One of the best APA's I've had is Tired Hands Hop Hands and they use massive amounts of oats with clone recipes suggesting close to 20% flaked oats.
I wouldn't use much in a typical dry west coast pale ale but it's perfect for the newer Northeast/Vermont style hoppy ales that tend to have a silky smooth body (usually low ibu's, very hazy, dry hopped like a 2xIPA, more chloride and less sulfate than usual, oats or wheat isn't unusual, and an expressive yeast like Conan or London Ale III instead of Chico).