I think that string theory, and it's alternative M theory, are most likely wrong. The concept of sub-microscopic strings giving rise to all visible matter by their vibrational patterns seems a little far fetched. However, the math looks pretty good (the parts that I understand), and the fact that theoretical physicists are willing to delve deep into the realm of 'science fiction' is a good sign. No longer are we holding onto outdated paradigms which have been unable to further theoretical physics, instead we're finally starting to use our imaginations. So even though string theory is MOST LIKELY wrong, it's a leap forward in our mode of thought.
If you want to read up on string theory, one of the best books available is called 'The Elegant Universe' by Brian Greene - it also gives you an excellent simple description of einsteins general and special theories of relativity and quantum mechanics. If you're interested in physics, this books is a must read!