We've had invetive themes and not so inventive ones. My favorite to date was our Indian themed night - someone brought the most amazing homemade mango chutney! But we've also had 'Three Ingredients or Less', "Mediterranian", "Vegitarian" and this month's is "A Victorian Picnic" (and we've been told we can leave our petticoats at home).
I'd encourage anyone to get a group of friends together and try something like this. It would be fun to do as couples also (our husbands call cooking club 'left over night') and as families though the dynamic would be totally different depending on how you set it up. Family night might not be quite as gourmet :)