May I suggest these:
1. bragging rights 2. finding hot spots 3. posting a picture from the outing to keep a record of social activity
Why a new "specialized" social network?
I am interested in the fact that
1. it is only for females (the market segment that spend the most: http://techcrunch.com/2011/03/20/why-women-rule-the-internet... )
2. the network will grow from one initial person and would be possible to reach anyone from anyone (I am not expert in the science of graphs so this sounds interesting to me)