At the risk of contributing to what has recently been called the intellectual wasteland that is the physics blogosphere, I want to point out a nice review paper on the arxiv, and its connection to high energy physics. Subir Sachdev at Harvard has put up a relatively pedagogical review about quantum magnetism and criticality. Back when I was a grad student, I didn't appreciate that quantum magnetic systems were so interesting - I thought that they were a zoo or menagerie of semi-random compounds that happened to have effective model Hamiltonians of interest only to rather esoteric theorists. Now I understand the appeal - the relevant Hamiltonians can have some truly bizarre solutions that can be relevant (intellectually if not directly) to whole classes of systems. One class of such systems is the heavy fermion compounds that are non-Fermi liquids, and another comprises some exotic "spin liquids". The low energy excitations of these strongly correlated quantum systems are not readily described as particle-like or wave-like. They don't have simple quantum numbers and simple dispersion relations, and they result from complicated, correlated motion of electrons (or spins, or both). This has been known in condensed matter circles for some time, and is very neat. Much exciting theory work is being done to come up with good ways to treat such systems.
What I don't understand, and perhaps a reader can enlighten me, is how these ideas relate to "unparticles". Howard Georgi, also of Harvard, made a pretty big splash this past year by publishing a PRL (linked above in free form) about the possibility that there may be fundamental excitations of quantum fields (like the ones thought to be relevant in high energy physics) that are not simply described as particles. Since this paper came out, there are now 78 papers on the arxiv that deal with unparticles. So, is this a case of high energy physics reinventing an idea that's been known conceptually for some time in condensed matter? Or is there really a basic underlying difference here? I should point out that at present, while there is experimental evidence for non-particle-like excitations in condensed matter, there is not yet any evidence for such things in high energy experiments as far as I know.