Most readers are probably on top of this already, but if you’ve been too busy to check RealClimate you’ve missed an excellent piece by Ray Pierrehumbert, putting the Keystone pipeline controversy into a good quantitative perspective.
The short version is this; to have a 50% chance of staying below 2 C warming, we have only about 500 GT of carbon left to burn (assuming no major sequestration effort kicks in). The Alberta tar sands alone contain 230 GT. On the other hand, proven coal reserves worldwide appear to be about 634 GT. But on the other other hand, there is an argument for not encouraging new types of fossil fuel to enter the mix.