You're still talking about progressive enhancement though. There's a difference between using a user-agent check to find a very specific environment where a bu

You're still talking about progressive enhancement though. There's a difference between using a user-agent check to find a very specific environment where a bug will occur, and using a user-agent check to determine which of 3 browsers you accept. Used properly, user-agent tests can be a kind of adjacent form of feature detection. Used improperly, and your site is best viewed in IE, even though the user is on a browser that they know will work.