Searches by song and artist. For example, if you type in "willie" you are going to get songs by Willie Nelson as well as the song "Willie & The Hand Jive" (and several other songs/artists).
More is less. Using the example above, if you type in "willie hand" you will get "Willie & The Hand Jive" by a few different artists and "Healing Hands Of Time" by Willie Nelson.
Less common words work better. Using the same example one more time, if you type in "jive clapton" you will turn up just one song; "Willie & The Hand Jive" by Eric Clapton.
Partial words count. You don't need to type in full words. This can be especially helpful if you aren't sure of the spelling. For example "wil nel" brought up a complete listing of all Willie Nelson songs, along with one unexpected hit; "Love Will Conquer All by Lionel Richie".