When I have a race that it isn't obvious what it's alignment is, I NEVER tell ANYONE but those of my own alignment what I actually am. Though, people usually end up figuring this out, it most of the time, keeps my character safe for the early levels as most people don't want to piss off potential groupmates unless they're level sitting. It also, like WarEagle says, makes RP more interesting when you're avoiding those sort of questions or answering in riddles to confuse them and change the subject.