after having been refered to Lyle McDonals site by facko i read a few articles and i have to say it was pretty enlighting.
OP - listen to what he has to say. Or even better, go to the site yourself and read a few of the articles, you'll feel a lot smarter at the end it, i guarentee that!
With that said, i do still beleive that as aonother poster said, insulin plays a big part.
Basically, its hugely anabolic, in other words when its floating about your body in high amounts, your primed to grow, but unforetunaly not only your muscles, it counts for fat too.
Personally i take the approach of eating carbs strategically.
First thing in the morning, when insulin sensitivity is naturally at its highest, before training and after training to fill up or replenish glycogen stores. I usually aim for about 40g clean starchy carbs (not shitty sugar) before training and 60-80 post, again CLEAN!
Thats my approach, others will disagree and i'm sure some will agree. What you take from it is up to you.