1. Left
2. Middle
3. Right
4. Back
5. Forward
6. DPI
7. Alt-Tab
8. Play/Pause
9. Skip Track
10. Stop after Current Track
11. Vol Up
12. Vol Down

With a tilt wheel freeing up 4/5 it's possible to make otherwise awkward multi-key shortcuts a single press - particularly ones that would otherwise require taking a hand off the mouse then putting it back afterwards to complete, and that's without even getting into macros...