Jaykyu - thank you for spelling that out, I really didn't want to type it.
You actually go faster by not being in the backseat. By staying forward you can get your skis to ''run'' on the snow more effectively and you can (if you know how) accelerate through every turn.
Now I think there is a time and a place for everything though, I love cruising around on my tails (gets some great looks when you pass people with your tips 6+ inches in the air), but it is very easy to lose control of the skis.
Technically, there is absolutely no advantage to being on the tails of your skis (I'm not trying to start an arguement here either, so please don't think I am). And for those of you that think that you need to be back a little in powder, you are just hurting yourself, it is muscularly more strenuous, you have less control, and basically leaning back in pow is the beginers philosophy. Your best bet is to remain centered (balance) and keep your feet more under your body, using more turning of your feet to turn, and less angulation.