Michelle Thaller at the CS Monitor has a very nice article about rethinking the rules for formation of planets around stars. Our solar system is organized with rocky planets inside and gas giants outward (plus Pluto and planet X), and I remember being taught that the pressure of solar radiation tears the bulk of gasses off of planets whose orbits fall inside a certain radius. (Another idea I remember is that Jupiter formed at the orbital distance corresponding to the condensation point of water in the primordial dust cloud.) But the Spitzer telescope and other search methods are finding lots of examples of big gas giant-like planets very close to their star, along with planets orbiting brown dwarfs and a fair number of systems which likely resemble ours.
What I love about this is that the science is getting outside of an n=1 (our own system) and really sampling what is available in nature's palette. The next decade or so should be very interesting.