Another good use was pointed out in the excellent TEDx talk (https://bitcointalk.org/index.php?topic=115555.0):
the ultra poor -- those who have no means of establishing financial arrangements with banks and have no safe place to store their money -- could use Bitcoin not only as a bank but also as a global payment system. 

No doubt the cash like aspects of Bitcoin do encourage cash like use, especially in the same illegal ways cash is used; but to fail to see the global, society changing differences Bitcoin has from cash I think is short sighted.  Bitcoin is a bit more than drugs, porn, and guns.