Phi Sigma Pi is coed. (We're officially an honor fraternity, but with a lot of social aspects -- kind of like greek for geeks.)
I love PSP being coed! Both my big and my little are guys. Intra-brotherhood dating does happen, like for example I've dated brothers, and also this summer my big is getting married to another PSP brother, but brothers do mostly respect each other enough to not randomly fool around with other brothers from the chapter. (Now I'm not saying anything about what goes on at interchapter events and national convention...
)
It's a different dynamic from a social sorority/fraternity, for sure, but I like it. I like how my chapter of PSP's planned social activities range more into the air hockey tournament / laser tag / restaurant hopping outings, as opposed to AXiD's sisterhood activities which are more of the whole chick flick / makeover night / going out for ice cream kind of thing. It's different and fun.
As for what Tom said about waking up in the mornings -- we don't have a house. I don't think any PSP chapter has an official house, although brothers will often rent a house or apt together to live in, sometimes coed, sometimes single-sex.