The dbus-cleanup-sockets command cleans up unused D-Bus connection sockets. See http://www.freedesktop.org/software/dbus/ for more information about the big picture.
If given no arguments, dbus-cleanup-sockets cleans up sockets in the standard default socket directory for the per-user-login-session message bus; this is usually /tmp. Optionally, you can pass a different directory on the command line.
On Linux, this program is essentially useless, because D-Bus defaults to using "abstract sockets" that exist only in memory and don't have a corresponding file in /tmp.
On most other flavors of UNIX, it's possible for the socket files to leak when programs using D-Bus exit abnormally or without closing their D-Bus connections. Thus, it might be interesting to run dbus-cleanup-sockets in a cron job to mop up any leaked sockets. Or you can just ignore the leaked sockets, they aren't really hurting anything, other than cluttering the output of "ls /tmp"