I took lsd for my first time when I was 18. Previous to this I had never taken any drugs except minor drinking of alcohol. I had a GREAT time because I went into it with no regrets, no predispositions, and as healthy as could be, also I had researched it a bit in high school and written a research paper on it.
I took two hits of blotter, probably in the 50 mic range each (based on further doages of the same batch), and me and my "guide" who was sober went to a dance club. FANTASTIC experience.
Since then I have used it ~50 times, usually a month or more apart, and have NEVER had a "bad trip" nor any negative flashbacks. This drug is ALL about set and setting. If you are confident in your abilities to think things through, have prior knowledge/research on what you are about to partake of, and don't mix and match for your first time, then I say GO FOR IT. I personally believe a 100 mic dose is no problem for a first time user if the above ideals apply to you.
I have never taken more than 300 mics at once, although at that level it is a pretty incredible journey. It has been 10 years since I had any, and I am pursuing a source...w00t!!!!!