So, tonight I bought some poker chips (and a deck of cards for an unrelated game I'm designing) for use in the Star Wars game. Every person got 2 blue chips and 1 red chip, representing their Force points for the session. The red chip, however, represented giving in to the Dark Side... using a red chip increased your Dark Side score by 1, in addition to the benefits of a force point.
Overall, it went very well. People used a lot more Force Points (I found in previous games that they tended to sit unused), and tended to suggest novel uses for them, some of which I allowed.
In addition to the standard "Add 1d6 to a given roll", I allow:
1) Add 1d6 to a given defense for a single attack.
2) Subtract 1d6 from the damage of a single attack. If the damage is to be halved (for example, folks were free with grenades this evening), this applies to the raw total, not the final damage; so if the bad guy rolls 14 damage with a grenade, and you roll a 4, you take (14-4)/2 damage, not (14/2)-4 damage.
3) A red chip may be spent for a single use of a dark side power. This will result in an increase of 2 to Dark Side score... 1 for calling on the Dark Side, 1 for a Dark Side power.
I also wound up PLAYING with the red chips a lot. Holding them up at appropriate moments. Turning them over in my hands. Because even when players spent them, I let them keep them. You can pour as much Dark Side as you like into an action if you REALLY want to succeed.