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Wow, I just found out something! Brian Greene, author of The Elegant Universe, along with Discover magazine, held a contest for a person to describe String Theory in 2 minutes.

Go to youtube at this address

]http://www.youtube.com/watch?v=fvBW_8Jw8Lo

Brian Greene was one of the people who wandered the halls when we were attending the Society of Physics Students - this was back when I was a physics major at Columbia U. My thoughts on string theory are like this:

1. what is it that is vibrating? Clearly "string" is not the answer, so what is the substance of this vibration?

2. if the substance vibrating is 1 dimensional, in which of the three spatial dimensions does this substance intersect? By what method does this 1 dimensional object multiply by infinities to produce higher dimensional embodiments?

3. where in spacetime is the string vibrating, on a plank scale, or an infinitesimal scale? How does string theory resolve itself with Plank units of space and time?

4. what are the mechanics of motion causing the vibration, and if in 1 dimension, what measure are we using to attribute vibration - which by its very definition implies motion from one point to the next in a system of oscillation?

The strings themselves are not really "made" of anything in that they are supposed to be the fundamental blocks of existence. You can liken them to fields (in the quantum field theory sense of the word "field") only the field is general enough that it can support multiple types of particles.
While the strings themselves are 1-dimensional, they vibrate in 9 spatial dimensions (10 if you're to believe in the current speculations about M-theory) mostly because of stability issues. Fortunately, we don't expect the strings themselves to give rise to the various dimensions, only to the particles that exist within the universe; the dimensions, and indeed the entire background on which physics takes place, is considered an external object in string theory.
The string length is actually supposed to be one of the three fundamental parameters according to string theory, along with the speed of light and Planck's constant. The length of the string should be around the Planck scale, but definitely non-zero. The strings are able to operate below the Planck scale on the assumption that the Planck scale only is meaningful in terms of observation; you can't observe below the Planck scale, but space isn't actually discrete.

I've never really liked string theory. I'm a big fan of general relativity, and so the fact that string theory takes a completely different, and indeed completely incompatible, approach to gravitation bothers me a lot, even beyond the rather ad hoc nature of the theory, the dismissal of rather blatant convergence issues, and the 10^500 possibly nonequivalent vacuum solutions.
The basic problem is that string theory has a specific, fixed, flat background of spacetime upon which it operates, and gravity arises due to particles that carry quanta of gravity such that objects that carry energy exchange gravitons and thus are attracted to each other. General relativity, in contrast, operates on a dynamic spacetime intimately connected to the things on it and thus is formulated in a way that isn't dependent on the background; in this case, gravity manifests as the warping of spacetime. Trying to combine the two leads to unrenormalizable divergences, in that it would take an infinite number of correction terms to prevent the most basic of interaction calculations from becoming all infinities. This happens because the warping of spacetime then changes the coordinates by which energy and action are measured, screwing up the second quantization process beyond repair.
Quantum mechanics/QFT doesn't have this problem, but that's because it is only applied on the low-energy limit where gravity has basically no effect. If string theory is to be a full theory of quantum gravity, it's definitely going to have to be able to tackle the cases where gravity becomes nonperturbative.
Supposedly M-theory won't have this problem, in that it is supposed to be background independent the way general relativity is. I'm not entirely sure how that is supposed to work, considering that the quantum Hamiltonian as currently expressed is very, very background dependent, at least in spatial/temporal coordinates. I guess if it takes a lot of the ideas from topological quantum field theory, wherein the exact coordinates don't even matter, M-theory might be able to become background independent.

I'm more interested in the relativity-inspired attempts at quantum gravity, like loop quantum gravity or twistor theory. They're naturally background-independent, although they require almost completely giving up our notions of what time and space are. Unfortunately, expressing the Hamiltonian formalism and the physical constraints has been less successful in these cases than with string theory.

In M-theory, the graviton formulation of quantum mechanics and the spacetime deformation formulation of general relativity are supposed to coincide somehow, in that gravitons become packets of spacetime deformation. Again, I'm really not sure how this is supposed to work.