What kind of data is stored in /data/user directory? It seems to store some kind of application data, but how is it different from /data/data directory?
/data/user was added in Jelly Bean as part of multi-user support. Each user on the device gets a directory in there named after their user ID, and that directory contains each app's data directory for that user. /data/user/0 is a symlink to /data/data.