Never did acid, but I tripped a few times on shrooms and I had a fantastic time, except maybe once when I was under stress. I didn't have one of those infamous "bad trips", but I felt uneasy. Just make sure to do them when you are not worrying about anything, a friend of mine did totally flip out. After a couple of years you just look back and laugh about it, but at the time he thought he was gonna die. I never saw anyone have such madness in his eyes as then.
Anyway, shrooms can be really awesome. Do it with a couple of good mates, try to stay indoors or at least some place quiet, make sure you won't be disturbed by other people and get good food, good music and whatever entertains you. Enjoy!
Oh by the way, they do taste like old man socks, so if you want to avoid an upset stomach, just brew tea with them. It's what we did and it works just as fine.