I would encourage you to consider sending people to a completely new URL instead of loading the lyrics with Ajax, unless the browser supports the HTML5 History API.
That way, people who use modern browsers get the original user experience, but those who use legacy browsers have to see a quick refresh. Your site is so clean already that I doubt most IE users would notice the load time.
As an alternative, support hashes and the history API so most people see the "clean" URLs.
You might consider using real query URLs such as /?q=query or /q/query , and using the HTML5 history API to load those query URLs via javascript without changing the page. That gives you unique URLs without just using anchors, making it feasible to index.
