Quoting Mike Hearn <mike@...869...>:
The term copyright assignment isn't mentioned, they still seem to be figuring out what they can/can't/will/won't do with the code once it's been released.
It's worth remembering there is a middle ground: it doesn't have to be copyright assignment for them to be able to use your code.
The alternatives would be requiring dual-licensing for contributions, or using a license like BSD or (for those things you can break out into libraries -- see my other post) LGPL which would permit linking against the Pantone et al libraries in the commercial product.
You just have to figure out what is acceptable for both parties and then agree to it in writing. I guess if you're happy with the way your code is being used and therefore aren't interested in suing them, who owns the copyright matters less.
Making individual agreements with contributors isn't practical.
-mental