A really nice site. To give you an idea of what it does, let's take "Uncle John's Band". Under that entry, they have the lyrics, and hyperlinks at some of the words take you to footnotes at the bottom of the page. For example, in the lyrics "God damn, well I declare / Have you seen the like? / Their walls are built of cannonballs / Their motto is 'don't tread on me
'", the italicized words take you to an entry at the bottom that tells you that "don't tread on me" was an American Revolutionary War motto.
Overall, the site author does a nice job with the references, and Rober Hunter's lyrics are especially good for this sort of thing. He also does a nice job of steering clear of trying to interpret the songs--he provides mostly unbiased hints by defining certain obscure words or phrases, and by explaining the more cryptic references. Very nice. If you like the Dead, you might find yourself some time here.