The effects of Psilocybe mushrooms are similar to a mild LSD 'trip', that is, they alter the perception of sight, sounds etc. and change the feelings and thoughts of the user. They take effect after about 30-45 minutes, peaking after about 3 hours, and last for around 4 or 5 hours altogether.
At low doses euphoria, a sense of well being and a feeling of detachment occur, along with some mild distortion of perception. There is less dissociation than occurs with LSD and so less chance of a 'bad trip' as the user still has some control over his or her thought processes. Nevertheless, the effect of psilocybe mushrooms is unpredictable and depends on the setting in which they are taken and the mental or emotional state of the user.
At high doses visual distortions and vivid hallucinations can take place.
Most mushrooms containing psilocybin cause some nausea and other physical symptoms before the mental effects take over.
Source: http://www.recovery.org.uk/druginfo/index.html
Willie Nelson bragged about playing golf on acid one time (well, he went out on the links, don't know that he was actually into the game he was playing that day).
Here in Texas they sprout up out of cow patties after a rain...I'd be more worried about E Coli......