I predict that LSD will become much more popular in the near future due to services like The Silk Road and Bitcoins. While other drugs can be detected quite easily in mail with scanners and such, LSD in plotter form can't be detected without actually opening every letter.
For people like me, who didn't know what "Silk Road" was in this context:
It's an anonymous market for drugs using Tor. [1] Bitcoins are used for paying.
