Indeed they do. However the dose they use in the psilocybin research equates to a much greater dose of mushrooms than the "average"(I'll assume 3.5 grams of dry P. cubensis) dose goldfishlaser speaks of.

The whole point with psychedelic drugs is that one must take a high, overwhelming dose in order to experience the full gamut of experiential states possible.

I have an excellent cognitive psychology book published by OUP called The Antipodes of the Mind:

http://www.amazon.com/Antipodes-Mind-Phenomenology-Ayahuasca-Experience/dp/0199252939

The book takes an empirical, phenomenological approach. The author has gathered data from around 2,500 experiences with the plant based tea Ayahuasca(in effects it is rather like mushrooms yet typically stronger). He himself has taken the brew well over 100 times. This data is then analyzed in various ways: semantic content of visions, progression and stages of the experience, structural topology of visions, and so on. Please take a moment to browse the table of contents in the amazon online book preview to get a feel for both the academic seriousness of this book as well as the quite fascinating contents. Best of all, the author, Benny Shanon, includes numerical tables and a whole appendix devoted to explaining his research methodology.