First, Rabett discusses the "quenching" phenomenon that explains why CO2 infrared absorption isn't quickly saturated here, with much more in the comments. I had never understood the idea that the energy from CO2-absorbed radiation is transferred by direct physical contact with other molecules instead of being re-emitted. The part I still don't understand then is whether saturation could ever limit IR absorption so long as there's plenty of non-greenhouse gas molecules in the atmosphere to do the quenching.
Second, the lawsuit against the California waiver that allows California (and many other states following California's lead) to set greenhouse gas emissions for vehicles is back on again, despite the automaker commitment not to sue. The auto dealers are suing instead, in a typical trick. I agree with Warming Law that this isn't a moot issue, despite the fact that the feds have now adopted California's standards. It's a backstop against something going wrong with a federal effort (or, gods help us, a denialist Republican elected president in 2012). It also reinforces the legitimacy of the Clean Air Act waiver process which has been granted in virtually all cases before it became politically inconvenient for the fossil fuel industry and their political minions. California may need to do this again in the future, so we need to keep the option open.