Chewing My Lower Lip

Ok, so bit of a dilemma.

The super cool job called me back for a working interview, and she suggested I come in this Thursday, the 27th. I said no, Thursdays I work, but another day would be fine. So, she said she would call me back the next day. I waited all day by the phone for it to ring , and I even called (the secretary said she'd call me back "momentarily").

It's been four (business days) since I've heard from her. There's still a chance she might call, but my dilemma is this: do I send a thank you note?

I always send thank you notes. If you're my friend long enough, you've probably gotten one, and I always send one for interviews I like. (I think it's a dying art and I'm trying, single handedly, to revive it.) But if I send one now, would it look desperate, showing that I waited by the phone for it to ring, or would it look polite and cool? I would have sent one, but she called me back for the working interview the very next day before I had a chance to, but I haven't heard from her since, and now I just don't know. I'd like to err on the side of caution, but I don't know what erring on the side of caution is.

So, dear friends: Send a thank you note or not? Comment or email or call me or IM me or whatever.