I've found much of the Keystone Pipeline analysis to be lacking.
One of the main arguments against it -- the potential damage caused by leaks of the particularly dense goop extracted from the Canadian tar sands -- is of course perfectly sound, especially given the environmental sensitivity of the planned route. But a) they'll just change the route (as TransCanada, the potential builder, has already announced), and b) this is kind of a NIMBY argument anyway. Why should we feel better if this stuff mucks up Vancouver, BC instead of Nebraska?
The more convincing arguments are those of climate scientists who warn that based on the magnitude of Canada's tar sands deposits and the energy needed to extract oil from them, this stuff will dangerously accelerate global warming. Here, the work of the reliably correct James Hansen is... um... sobering, to put it mildly.
But there's a fundamental problem with this argument as well, and it's not with the science, it's with the politics. As long as this stuff a) exists in known deposits, b) is in demand, c) can be profitably extracted, and d) is not viewed as a global hazard for which there are safe, economic alternatives, then extracted it will be.
This piece by the New York Times usefully covers these issues. It quotes Canada's PM thusly:
"I am very serious about selling our oil off this continent, selling our energy products off to China."
And while the piece importantly notes that the Obama administration will likely not be jammed by the payroll tax/UI deal that insisted on a quick decision (i.e., the president won't approve it), it also points out that:
"...experts in oil economics say that the oil is coming out of the ground in any event because of steadily growing global demand and the heavy investment in infrastructure already made in Alberta."
That sounds right to me, and in this regard, the most important comment in the piece is by activist Bill McKibbon:
"Stopping Keystone will buy time," he said, "and hopefully that time will be used for the planet to come to its senses around climate change."
If that doesn't occur soon, then oil from the tar sands will flow, and it will keep flowing until we put a price on carbon or come to our senses, whichever comes first.