Hi there,
very interesting question!
I've researched this very briefly. By using jQuery at all any user is bound to the MIT License "within" jQuery:
http://en.wikipedia.org/wiki/MIT_LicenseSo if you want to be clean regarding legal issues, I reckon your license will have to be compatible with the MIT license. But on the other hand, it is a very liberal license, permitting re-use within proprietary software.
I don't know at the end of the day, but would be very interested in the topic, too, if someone else knows...
Arvind Gupta
jQuery Plugins:
http://4nf.org/