I guess I'm not sure what the fuss is, on both sides.
On the environmental side, these tar sands are being/ will continue to be developed, one way or another. Pipelines aren't fool-proof (plenty of evidence for that), but one could argue that it's a better method of transport than rail or by sea.
On the other side, even if the US approves the pipeline, that oil goes into the global market and will do absolutely nothing for the price at the pump at home. As well, while building the pipeline may create American jobs in the short term during its construction, the tally of permanent jobs seems awfully low. I suppose there may be a boost in profits for American refineries, but that doesn't help anyone you or I know.
I realize environmentalists want to make a stand about this particular pipeline, but again, those oil-fields will be developed one way or another. I think maybe the protest should move to Canada - it's their oil.