I use 4sq for two things -- keeping track of where I've been when I travel, and letting people know where I am when I travel in case we're near each other.
From this description, it sounds like I'll need two apps for that now. In which case I might as well just use a Facebook checkin and not use 4sq at all, since Facebook serves both purposes.
The two apps will also work seamlessly with each other, for the moments when you are making a plan for dinner with friends in Swarm app, you can click an icon which takes you to Foursquare app for search. And many more such interfaces.
But now the thing I use Foursquare for, checking in and finding places nearby are in 2 apps. Before it was ok if each part was good not great because having them both together was a win. But by splitting them the places nearby app is now directly competing against Yelp and Urbanspoon and others.
I'm not installing 2 apps for this, so the check-in part will likely not be done by me anymore. I might still use Foursquare proper, but only if it is better than other similar apps.