You can organize playlists by BPM and then practice in a particular BPM range to your music without getting bored listening to the same song over and over and over and over...
This free software allows you to batch process a music folder's tempi; this means you can analyze the tempo of a lot of files really quickly. Once you have analyzed the files, it then adds the bpm to the files so you can sort by BPM in an audio player like iTunes.