That's not sufficient to serve a Rails site though.
Rails is a great platform for building a custom web app, but it's a terrible platform for building an open-source blogging platform. It simply moves too quickly and breaks things too often to be useful for the demographic that uses WordPress.
When you're talking about web code with such an astronomical deployment to developer ratio, the advantages of PHP are magnified by several orders of magnitude. Even the perfect WordPress replacement written in Rails with elegant, featureful and performant Ruby code digitized by God's own hand is by definition a niche product that can never hope to compete meaningfully with WordPress.
I use Last.FM to find similar songs. It appears in the right sidebar when you play any song.
I didn't use Last.FM for the main search, because I couldn't get the album name directly from the keyword search (the JSON has the title and artist only). Getting the album name would require querying the API for each search result which again I tried but takes about 30 sec for the results to appear.
I am considering using Spotify's API though since iTunes gives strange results sometimes.