Haha, i should have read Welcome to the CHDK forum! (and RULES).
There is my answer: "developers should keep in mind this a GPL based project, so any publication made here should upkeep to the license's rules"
Note that scripts floating around on the forum or wiki are not necessarily part of CHDK. It's up to the authors to specify (or not) any license they want.
In general the community has not paid much attention to this for scripts. If no license is obvious, linking/crediting the source is always a good practice.