There is definitely a limit there. No matter how cheap or silly, as long as it doesn't seem cheap, if it came for free people will remember. The times I have been given something free that is particularly cheaply made, usually something made out of very low quality plastic, I always think "Oh, these guys evidently don't care about their users/fans/supporters, if they're going to give me something that won't last 10 minutes".

I think its important to give away things that are not your core business. I like the pandora hat and I remember it fondly, but if my coworker got a super-awesome pandora account, I think I would just feel "dang, why didn't I get one".