It's a tough problem – no doubt about it. In v1, as we expect your nearby network to be quite small, we've focused heavily on your existing friends network (from facebook) and are trying to make that experience as good as possible. Inviting them, organising the events, etc.
In the past, just like you, we used facebook groups and/or messages/chats back and fourth to friends.
Hopefully the app will be good enough for people to start out with their existing friends and then more and more people nearby will show up.
Chicken & egg. I once started with a similar idea - meeting sport buddies - but on a country scale. I found it very hard to gain enough traction for people to actually be able to meet each other.
Because.... what value does it bring for Joe who's living in SF, that Jane from NY wants to go for a work-out? I think "importing" events from other sites is one option to get things going (still - quite a lot of effort). Other idea - is to start locally, run a big ad campaign, get in touch with sport centers, etc, then "conquer" other cities, one by one.
In the past, just like you, we used facebook groups and/or messages/chats back and fourth to friends.
Hopefully the app will be good enough for people to start out with their existing friends and then more and more people nearby will show up.