Just was browsing erowid and I came across this, kind of cool description.
A GENERAL TOPOLOGICAL EXAMINATION OF THE SCENERY
Minutes after ingestion:
Usually the first effects of psilocybin are perceivable after ten or twenty minutes. Funny or strange things may pop into your mind. One may feel very relaxed or like jumping all over the place. Next you may feel like you were blasting off, up towards the stars, rising high. Chewing the mushrooms for about ten minutes in your mouth enables the psilocybin and its analogues to enter the brain faster - if the mushrooms are immediately swallowed, it may take as long as 1 hour for the first effects to set in.
If you get any physical symptoms, this is when they will hit. You can avoid or at least reduce nausea by not eating very much before the trip and not moving around too much during this phase. Throwing up is uncommon but not unheard of; having a barf bag around, especially on the first few trips, is a good idea. If you find that your body really doesn't like shrooms, a motion sickness pill (Dramamine and similar anti-histamines) beforehand may help. But don't worry about it too much, even if you feel queasy the nausea will end quite quickly.
40 Leaving the atmosphere
One will begin entering the realms of the experience; often the first real signs are simple hallucinations with the eyes closed or in darkness, little colored pixels floating around etc. If one is going to go to the toilet, it should be done now.
1 hour is usually sufficient for the more powerful effects to set in. The body will feel heavy and drowsy.
After two hours the peak of the experience. Often quite awesome.
By now one will again start to remember the concepts of normal reality and may feel like getting something to drink and eat, or talk and do some moving about.
After about six hours most of the effects have disappeared and sleeping becomes possible.
If you trip at night and fall asleep when the trip is ending, this is when you'll wake up... and the odds are you'll feel GRRRRRREAT!
7d Jet lag
Afterglow of the experience will persist anywhere from few days to several weeks; what you've learned may change your life. Occasionally this learning will be negative and you'll be depressed for a while as you assimilate the fact that you've been wrong about something for all your life, but the depression is never extreme and - cheezy as it may sound - you will be a much better person afterwards.
Surgeon General's Warning: One of the aftereffects of psilocybin (and most all psychedelics for that matter) is "emotional fluctuation", ie. things that would make you a bit happy cause euphoria and conversely things you don't like cause depression. At its worst this is a real manic-depressive rollercoaster, but usually the fluctuations are more positive than negative ("It's Monday morning and I feel GRRRRRRREAT!"). At any rate, this rarely lasts longer than a day or two, so don't worry about it.