| The essential nature of the fusor is a method for creating a large negative space charge in the center of some geometry, usually spherical, although not necessarily so. The grids described by Zarchon are the most common way to do this, and by far the simplest, but not necessarily the best way to go about it. Prof Bussard has posited in several patents and scientific papers that it is possible to create the same effect by confining a group of electrons in the center of the fusor device, with magnetic fields. This has the enormous advantage that you do not lose energy to collisions between fuel ions and the grids. Bussard is known to be working on fusor research with Tom Ligon, but they are keeping it quiet.
The nature of the fusor is, as has been noted by several theorists, to shift fusion from the thermal domain to the velocity domain, i.e. instead of heating some fusion fuel to a sufficiently high temperature and hoping it fuses, you accelerate and focus a population of fuel ions at a single region, fostering head-on collisions and therefore more fusion events per unit input energy, at least in theory. This means you can use fuels other than the really easy ones like deuterium and tritium.
The most interesting alternative fuel combinations are helium-3/deuterium and boron-11/proton. Both are aneutronic, meaning they do not spit out neutrons to make the reactor structure radioactive. The He3 reaction is by far the easier to do; however, the reaction products have widely divergent energies, which means that the energy has to be extracted with a thermal blanket and a heat engine. This is where the boron-11 combination becomes really attractive, if it can be done. All of its energy is released as three alpha particles in a narrow range of energies. Since alpha particles are all positively charged, it is a relatively simple matter to extract the energy directly to electricity.
The fusor has been commercialized. Prof. Miley, of UIUC (IIRC -- feel free to correct me) has teamed up with DaimlerChrysler Aerospace to produce a scientific neutron source based on the fusor concept. | 
