I love this movie too, and like Herbman pointed out, I thought it was cool that Cera was actually on San Pedro in the movie. I have a special connection to San Pedro as it was my first psychedelic, so this movie really hits home.
There is a certain sadness I feel when watching it however. There is always a transience associated with youthful ventures; I can't help but imagining the characters nostalgically reflecting on their intense experience later in life. Also I find it rather acute how the characters search for the cactus to get high with. This really reminds me of some people I know and even myself at times and the lengths we go to in order to alter our consciousnesses!
The scene when they are sitting around the fire also brings up a depression in me, akin to that of the period right before I go to sleep after I have been on a psychedelic journey. The day that the eclectic crew had has finally come to an end, and now it's "back to the grind" after they go to sleep and wake up. I can't help but feel sorry for the Crystal Fairy too, as I can just tell that she struggles with emotional, mental, and social problems regardless of how "hippy" and "free-spirited" she might seem.
I am still torn as to whether I support psychedelic representations in popular media. I know on one hand it is good to spread awareness about how people seek these substances and the reality of their usage, but for me personally the emotions this film bring up almost make me hesitant to journey with San Pedro again. Also San Pedro is kind of in a legal grey area right now, and it is still legal to buy in the store for home decoration. Movies like this could inspire more people to use it, authorities to take notice, and then try to ban it somehow.
But Michael Cera is a respected actor, so that fact that he would actually use San Pedro for the movie and publicize this fact demonstrates, I think, an artistic acceptance of psychedelic drugs. It's "okay" that Cera used it for the movie, as he is an artist, so hopefully this legitimizes, in the eyes of society and the law, the use of psychedelics for other artists too.
"Think for yourself and question authority." - Leary
"To step out of ideology - it hurts. It's a painful experience. You must force yourself to do it." - Žižek