If you're like me, you can't stand seeing the same artist or album listed twice in your library because there's an extra space stuck somewhere in the tag. I set this smart playlist up to catch all of the tracks in my library with extra spaces.
Match any of the following conditions:
Artist begins with <space>
Album begins with <space>
Song title begins with <space>
Artist ends with <space>
Album ends with <space>
Song title ends with <space>
Artist contains <two spaces>
Album contains <two spaces>
Song title contains <two spaces>
This is a good idea, especially with the incoherent rubbish you often get from CDDB.