Originally Posted by Freebase Dali

It's a lot like acid in terms of visual and auditory hallucinations. To me it has more of a body feeling than acid does, and feels more... earthy? Acid has a more electric/plastic feeling to me. I prefer acid, but shrooms get the job done.
They taste horrid, and you get a bout of nausea on the come up. There's a nice rush on the come up that's a little more tame than an acid come up, but you get the same general feeling.
On the peak, I tend to get strictly shroom-related CEV's (closed eye visuals) that differ from the ones I get on acid, but the intensity is no different.
The OEV's are somewhat similar to acid.
Auditory hallucinations are pretty similar... music sounds pretty intense at moderate doses of either substance.
Obviously you have to eat more shrooms than you would acid, but you don't have to eat very many. If you're of average size and weight, 5 or 6 mushrooms are enough to get you going well. I don't really know the dosage in grams.. when I used to take them, we used to go out and pick them from cow fields and spend an entire weekend frying our brains out.

If you've never taken acid, my comparisons will be rather vague to you, but it's hard to really verbalize and express the important aspects of tripping beyond the usual every-day explanation.
There's a deep *mind* aspect of it that only becomes fully realized when you actually do it.

Try out Erowid.org and read some of the trip reports for shrooms.
There are thousands.