Of all the forums (which is a many hundreds by now) that I've joined, almost none that offered joinable groups or social groups used them well or at all. There's maybe one example that did, but they could do a better job of making member know it exists... So personally I'm not a fan of adding a feature which most forums won't use. Considering there is some demand for it, I'm sure someone will make a mod or something. That "other" software has it built in and makes such a big deal about it, but I don't understand why.