Lunch time… 
Usually I used logical-routers for testing purposes.
JUNOS supports 15 logical routers. So, using 2 routers you can have 30 logical routers.
Logical router is different with virtual routers.
Logical router has separates process between one another including the main router. So, we can treat logical router as different routers than main router.
How about virtual routers?Virtual routers processes are not separates with main router. If you have to do route leaking, you can use virtual router. You can see the complete documentation about logical routers in www.juniper.net.
