I think there was supposed to be a way to link to FB profiles but the feature had to be removed for some reason, which was probably why you couldn't download iTunes 10 until much later in the evening.
Facebook opens the API up for minor use, but major use of the API (and thus server laod) requires an agreement with FB. Apple and FB couldn't agree to terms, despite Apple demoing it at their press event. Each are blaming each other, but until it gets worked out, there is no FB integration in iTunes 10.