I think that it depends, of course, on the person. However my best guess would come from Dr. Bernstein's Diabetes Solution. He states that to keep blood sugars at healthy levels, one must consume no more than 6 carbohydrates in the morning, 12 each lunch and dinner, and a few at snacks. His recommendations are for long term (i,e. if a type2 is cured of diabetes, then they continue the same regimen to stay healthy and lower their overall insulin levels since low insulin levels are correlated with low incidence of heart disease and inflammation, among other things). I think that his wisdom, therefore can be applied to non-diabetics as well.
Disclaimer: I haven't read Dr. Bernstein's book yet, but it is next on my list.. I am having trouble getting it from the library.
Another thought: A lot of doctors toot different levels they think are healthy, so maybe the best way to determine for you is to get a A1c level test to see what your blood glucose levels have been for the last 2-3 months. Most doctors' reference ranges might be on the higher side of healthy, though.
I should do more research on this... if you look into this let me know what you find out!
I personally believe less than 30/day for a small woman and less than 45/day for a large man is ideal... with adequate meal spacing, but I am always learning.
Hope this helps!