Special Interest Groups

At the upcoming ExComm meeting on Sunday, the ExComm will be setting up guidelines related to SIGs. What do you think should be part of those guidelines? Also, what is the "essence" of a SIG that should be the definition that's used? Should it only be literal - special interest groups? Or should SIGs also include some sort of status within the acceptable types of SIGs, such as age, race, religion, gender, and sexual identity? (Note all of these do and/or have existed to some extent on both the local and national levels.) If yes to the latter, is there anything that would fall into those categories that would actually "cross the line" in your view? If so, what, how, and why?