Spin Foam Vacuum dynamics
Lee Smolin's lectures are actually very good. A lot of the mathematical background can be found in the papers he cites, and some of the basics are dealt with in Penrose's Road to Reality. Penrose of course came up with the spin network.
Loop Quantum Gravity suggests that gravity is mediated by a spin foam vacuum, and this is the main rival to string 'theory'. String 'theory' is an empty frame work to describe an unobserved graviton theory using unobserved 10/11 dimensional spacetime and predicting unobserved SUSY (super symmetry) partners. There is no effort in string theory to describe or model anything observable, and the claim that it predicts gravity is empty, as it just predicts and unobserved gravity mediation scheme, without any dynamics. Loop Quantum Gravity is completely different. His recent two lectures at the Perimeter Institute on 18 Jan, Introduction to Quantum Gravity, are available on line if you have a fast internet connection.
There is very little easily digestable material about Loop Quantum Gravity. Christine Dantas has a blog with useful references: http://christinedantas.blogspot.com/ Lee Smolin's lectures can be found here (you have to ignore the main screen and scroll down to the Introduction to Quantum Gravity at the bottom of the left hand side menu).
He starts off with spatial topology, sets of all graphs possible with or without edges, embeddings in all possible graphs, valent nodes on graphs (by analogy to chemistry, I presume). He defines Hilbert spaces on an orthagonal basis, then Penrose's 'spin networks'. Finally he shows how Feynman's 'sum over histories' approach to quantum mechanics arises in the vacuum: each interaction is a graph and you sum over all the graphs describing interactions in spacetime to arrive at the 'sum over histories'.
Smolin's second lecture dealt with 'background independence' which is the problem with special relativity. I think the recent comments of Smolin make 'background independence' clear: you don't worry about how to write the metric. Motl sees this as key to SR, unaware that the testable results of SR were available from electromagnetism of FitzGerald, Lorentz and Larmor, and even E=mc2 can be obtained from electromagnetic theory.
String theory only connects different bits of unobservable, untestable, speculation:
(1) 10/11 dimensions (Calabi-Yau 6-d manifold, Kaluza-Klein 5-d spacetime),
(2) graviton (spin 2 gauge boson) speculation (falsely called "predicting gravity" by Motl and Witten, when in fact it is unobserved speculation, and string theory can't make any testable prediction of the strength of gravity or anything else)
(3) SUSY super symmetric partners. Again, an unobserved speculation, with no definite quantitative predictions to test.
(4) The "Landscape" of 10^500 vacua, one of which may be real.
String 'theory' doesn't exist or have any program to deal usefully with anything that does exist.
The vacuum does mediate force, it does have gauge bosons in it (we know this for electromagnetism...), so some kind of spin foam vacuum is real.