How precise can OSM get?

In what data structures are the nodes' coordinates stored internally in OSM database (64bit floating point, some long integer, something else entirely...)?
What is the minimal distance that can be recorded without two points being rounded to the same location?
For gps recordings with accuracy in meters this will hardly be a problem, but as the map gets more precise, it might become one.

Obviously the longitude precision will vary between equator and poles, but still it would be good to know what the range is.