How to access gvfs mounts from command line?

Since Ubuntu 12.10, gvfs mounts can be found in /run/user/<uid>/gvfs.

Where /run/user/<uid> is the value of env $XDG_RUNTIME_DIR

As Eric's answer says, it also applies to 14.04:

It is in /run/user/<uid>/gvfs instead of /run/user/<username/login>/gvfs.

Please note that:

<uid> is user id = number

while

<username/login> is a string, human readable user name

Where one to the other is mapped through /etc/passwd or any other nss module (e.g. ldap). The numbers is actually stored on disk while the name is just for humans :-)