I've checked out this friendship party 3 times in the last 6 months. Generally there are 200 to 300 people there. I haven't made any long term friends from that particular event but I have been at least getting out.
They claim on their website though that they are going to expand to L.A, N.Y., S.F. London, Paris, Hong Kong and more. I wish them luck. Although it would be cool if it works, I think there are big differences between those other places and Tokyo. In Tokyo, things almost never get rowdy or out of hand and people don't vandalize. I expect that's not true in most other cities.