Where does the Messages beta pull my buddy picture/user icon from? I'm using the new Messages beta with my Gmail account and my iMessage account (which is linked to the same Gmail address). It's using a photo for my buddy picture that I've used before on various things, but I can't figure out why it's showing up here. It's not the picture associated with my Gmail account or my user account on this computer. I can't find the setting in Preferences where I can select a buddy picture, so it must be pulling it from somewhere in some account. 

So: where does Messages get its user picture from?
Gmail may be set to synchronise with your Address Book.  Go to your address book, and select the "me" card that you will previously have chosen as your own identify within Address Book.  Whatever picture is being used by your "me" card (or potentially by whatever card has a matching email address as the one your messages app is linked to) should be the one Messages uses.