In 1996 there were 250 academic journal articles published about marijuana, and in 2008 there were 2100[1]. In the US there are a handful of marijuana trials going on, but it's still very difficult to get DEA approval. I was at the MAPS conference this past weekend, and they were saying that to get approval for their psilocybin and MDMA research it was generally taking 2-4 years per study. And since marijuana is also schedule 1, the approval process is probably comparable.

[1]Source: Claudia Little in Psychedelic Salon podcast 218: http://bit.ly/doBrGA.