Watching the 60 Minutes talking about the importance of sleep(saying that lack of sleep may be related to obesity and some psychotic diseases) did give me some insight into how much sleep I should give myself.
I used to think that I do not need that much sleep, not as much as 9 hours people said in those science reports anyway, that it is quite necessary to eliminate some of my sleeping time for higher productivity, to get more things done, and to be competitive with my fellow colleagues who, well, sleep 4 hours a day.
But now it's occurred to me that indeed I am not a working machine, I am 100% human that sleep does play an essential role in my biological health, and thus, my productivity. It could be the 2-3 extra hours of sleep that actually lead to higher productivity instead of the lack of them. I used to sleep 6 hours a day and to be honest, in those days I didn't feel about myself as good as I do now, with 9 sleeping hours per day. I might lose a couple of working hours, but now I can actually wake up with a fully conscious mind. Unlike the past when I sometimes drooped in class, I can kick start my work right after getting up. It simply feels different. Surely I have not conducted any scientific research regarding the issue, but I can say I feel more productive than before, even though I work for less hours now.
My conclusion is that, well, while it seems to be a trend for people to sleep less and work more, saying that you can achieve more and get more things done, it is not any close to the (very scientific bullet-proof)truth that you shouldn't really scrimp on your time for sleep. The price you pay behind with sleeping less could be physical health issues like obesity and fatigue, and even mental ones like stress and depression, and most importantly, giving your sleeping hours away does not necessarily lead to increase in productivity, or worse, you might just get less things done with more things screwed up.
If you feel uneasy spending two hours more sleeping instead of working, fearing you might be "left behind" or whatever, you could just try it out during long holidays like I do. You might be surprised, you know.