ANONYMOUS Absolutely easy, simple and effective for it's purpose.
Because it is a widget it is alway ready, allowing to set the BPM of the current song in a few seconds. (Version 0.2)
ROLLANDBURN 1. Install widget
2. Play song
3. Hit F12
4. Click mouse to beat 10-15 times
5. Click 'Set'
6. Notice iTunes now has updated BPM column.
Simple pimple....to automate this process instead of doing it manually is the next best thing. Maybe I would prefer to hit the space bar instead of the mouse button but, meh, it works. (Version 1.0)