NO2 and L-Arginine are a couple of products that everybody seems to be wondering about. Does it really do anything besides giving you a great pump. Take a look at this article (http://www.bodybuilding.com/fun/layne35.htm) by Layne Norton.

I agree with the part of the article that suggests taking it post workout to increase protein synthesis. Personally, I don't take it for the "pump" effect, I take 4g post workout for the increased protein absorption. I can't say whether or not it's really doing much, though... I never really did any real measurements or number crunching on it.