On my campus, affiliate orgs are seen differently depending on the group. We have Delta beauxs and sigma rhomeos which noone really takes seriously. We also have alpha sweethearts and kappa sweethears and iota sweethearts. The only "acceptable" group to sorority girls is the alpha sweethearts, since most of them were once a-sweets themselves. The other two are looked at in a negative way, called sluts and all that, for what reason I'm not sure. On the incorporation issue, it seems a lot of the guy affiliate orgs have taken that step. I myself am not greek, but I found these two sites to be a little over the top:
http://members.tripod.com/~BEAUXINCFAMU/home.html
http://members.tripod.com/~Enigama/rhomeo.html