Basically, you can hold your iPhone up to a speaker that is playing music and the App will look through a DB of 5million+ tracks and match the music to the artist, album and track name, then you can buy the track straight away via iTunes, now thats cool IMO.
http://www.shazam.com/music/portal/page/default/template/pages/p/iphone.html
"Already an industry standard, Shazam fully integrates with and complements the iPhone's native environment, allowing you to seamlessly discover, buy and share tunes simply by holding your iPhone to music for just a few seconds.
Key user features:
- Tag music: identify music anywhere - whether it's on the radio, TV, in a movie or in a store.
- Build your own soundtrack: see the list grow every time music is tagged.
- Get the music: go straight to iTunes to preview and buy.
- Music Videos: see related videos of the track on YouTube.
- Capture the moment: personalise the tag by taking a photo and adding it to 'My Tags'.
- Share the moment: send track details to friends via email.
The Shazam application enables you to tap into a vast database of nearly 5 million tracks giving instant satisfaction for those times when you want to know the tune that is playing, learn more about the artist, buy the song immediately - or simply add it to your playlist."