Good question and one that deserves attention. Particularly if the rumours are true that Foursquare is talking with Apple Maps about data sharing. As they are using OSM themselves, it would not be particularly fair if they only allowed our competitors to use their data.
No, they haven’t released any of the data for places yet. And it is not required for them to do so. You can use non-free data as an overlay on OSM maps if you want.
And any sort of bulk import from FourSquare to OSM would probably be a bad idea.