Aspartic Acid does a hell of a job of increasing steroidogenesis in the testes. It's no joke, and is used as a pharmaceutical preparation in Italy, where the initial tests proved such dramatic results.
Two big downsides for me:
1) Diarhea. Just goes right through me. I am planning on making an injectable form soon that will kick some major ass, instead of making me blow major ass.
2) It also increases a bunch of other hormones, like prolactin, estrogen.
My advice is to use it for as long as you feel benefits. Don't over do it. More is not better.