So I've been using the new app for a few weeks (I was in the early test group), and it's doing at least half of what Foursquare wants it to.
The home screen that shows your friends in rough groupings of proximity (500 ft, 1 mile, 5 miles, 20 miles+ away) definitely makes it easier for you to see who is nearby at a glance. Not too many people were using the new app, so it was hard to tell if the neighborhoods check-in feature is catching on.
I still feel creepy hitting people up just because I saw they were nearby on Swarm. It's still a check-in app for me. Last Sunday it was totally beautiful in New York, and after finishing up a way too long lunch with my Mom, I wanted to HANG OUT. I went for a ride on my bike and at one point, I pulled out my phone. Sure enough, lots of my friends were hanging out in the parks and bars near me, but I felt weird being like "YOOOOO I SEE YOU LIKE A MILE AWAY!" Instead, I texted friends who I knew lived a few blocks away because that felt more natural.
Definitely still too early to tell for sure with this app, though.