Admittedly, this post is a bit off topic. But, if you enjoy playing guitar, please read on...!
A couple of weeks ago at ISMIR, I ran into Bas and Pedro, two of the guys behind Chordify. They gave me a little demo of what Chordify can already do and how simple and intuitive it is. I was impressed! Really cool stuff!
In essence, it lets you either upload your own music files or simply pick a YouTube video for it to analyze. After analysis, it spits out guitar tabs for the song in question. And to make it really easy for you, the user interface offers a player that visually shows you where in the piece you have to play which chord, i.e. the playback is synced to a kind of note/chord sheet. And it's synced both ways. In other words, you can start the player and an indicator will show you which chord to play. But you can also simply select a couple of bars and have the playback loop. This makes perfect sense, if you want to concentrate on practicing only a difficult section of the song.
Anyhow. I think this is great website. Check it out!