Physics applies to all objects and forms of matter: bicycles, cars, a biker riding behind a semi, etc.  Drafting is a distinct advantage for the person behind.  It turn, the law of conservation of energy states that energy can't be created or destroyed within a closed system.  Basically, some of the energy gained by the back rider is transferred through wind resistance to the front rider, which causes him to lose speed/energy.  (Example: put a tennis ball in a swimming pool about 5 ft. from the wall.  Pull water back toward the wall and watch the tennis ball come back toward the wall.  Same effect works here.)  Riders who work in pace lines can effectively ride faster as a group by trading off turns taking the lead.  Riders in the front work harder, then peel off and get a "rest" while they ride behind others.  I'm not that familiar with NASCAR, but the same concepts apply.  I hope this helps.

Well, the rider in the back doesn't literally pull the person back, but they do change the contours of the wind around the front rider.  If you study aerodynamics, you will find that the wind contours behind the object are also important, and I believe that the rear rider will make those contours more turbulent.  Even despite this, a pace line will work best because the front rider will be able to work harder for a shorter amount of time while the others "rest."  Then, a rested athlete will take the lead and push the pace.  In turn, the net physical effect is much stronger for the rear riders.  You are right when you talk about the psychological effect.  Clearly, this factor can be stronger than the physical effect, but I believe both are present to some extent.

My reply to drafting is that I've always had somewhat of a phobia about it.  I know what it helps you to stay up with the faster riders and reserves your strength, and I know that riders are supposed to switch places.  This all works fine and well if everyone rides close to the same speed and level.  I am probably more at an advanced beginner or intermediate level rider.  My experiences with drafting have been both good and bad.  I am afraid that if the rider in front of stops suddenly, I will hit them and go down.  See my post on the first page about road safety ettequotte.  In our group a new rider just getting used to clips the first day out, was the front rider. Three riders went down when a car passed a truck illegally.  Everyone in our group except for those actually involved, blames the girl in front because she stopped suddenly.  Three other people fell but not her.The first guy touched her back tire,  he suffered a broken collar bone. The second rider showed up just to visit a week or two later with his arm in a sling.  The 3rd guy just fell and sratched his bike.  I personally hate to be that close behind someone, especially a novice rider, and take a risk of falling

From what I know, the lead rider shouldn't be affected by those behind him because how drafting works is this: the front rider creates a low pressure air stream around his/her body because while he's moving, the air in front of him/her is pushed around his body. This curve of air is moving at a faster speed than the air around in, thus creating the low pressure system.  And because fluids always have to flow from a high pressure system to a low pressure system, the air around biker's air current will want to pull towards the rider, carrying anything with it.  So what's really pulling the riders behind the leader is the air around the rider.  Or actually, the "correct" thing to say would be that the air around the following riders is "pushing" the followers towards the leader.  (remember, this knowledge has been limited to my sophomore physics class last year)

Pathen

I think Jkenny5150 brought up a really good point about relativity. While the tailing riders may not slow the leader down in pure speed &/or energy, they certainly are riding at the same speed alot cheaper, and thus have the ability to overtake him/her down the road with much more in their reserve. I think that's the real point about drafting. That's my take on it anyways.

You all have it wrong!  You sit on a riders wheel so that he knows he is doing the work and you are just going to come around him at the end when he is tired and you win the sprint. Why would he want to tow you and do all the work only to be too tired to win at the end? That's why when a rider who is trying to break away has someone sitting on their wheel they will sit up and wait for the pack.

Oh yes , if you are talking pure physics, it is actually MORE aerodynamic to have another rider behind you, the rider behind acts like a rear fairing for the front rider.