I don't think that a bear canister alone is going to keep my food safe. However, I've never had a bear incident with my food and I suspect there's a good chance I've spent as much or more time camping in Yosemite Valley than anyone on this site. So, I reckon that I must be doing something right.
Let's pose this hypothetical question: If weight and size were not an issue (say you were car camping), and you weren't camped near any cliffs, and you had a canister and an Ursack at your disposal, which one would you put your food in for the night? I bet most people would pick the canister.
That doesn't mean it's a bad product... like everything, it has its plusses and minuses. You just have to weigh all the factors: Am I capable of tying the knots correctly? Am I in an area where the bears are active and proficient lock-pickers or am I in an area where I rarely encounter bears? What are the consequences of losing my food? What are the consequences of a bear getting my food? How much weight am I willing to carry - a canister, an Ursack, or nothing at all?
I still fail to see why the NPS would disallow something like the Ursack without reason. I highly doubt they're getting "campaign contributions" from all the bear canister makers out there. Their desire is to keep bears from getting food and it seems the burden of proof falls on the shoulders of Ursack or any other manufacturer of a new product to demonstrate that their product, in the hands of the average user, is sound. Maybe the Ursack IS just as good as a bear canister if the knots are tied properly or the bag is anchored properly... I don't know. Maybe the mode of failure is indeed user error - and that's frustrating for everyone out there who thinks they can use them correctly - but I listened to the recording of that court session a few months ago and even though I was rooting for Ursack, I didn't get the sense that the NPS was being unreasonable. It was clear that the lawyer and judge had no knowledge of bears or the technical nature of kevlar - they were just looking at the numbers and the bottom line - keeping food from bears. I guess I have enough faith to believe that they ruled this way for a reason. I certainly hope that Ursack can gather more evidence or redesign their product so we can get an alternative to canisters.
And remember, don't leave your canister near the edges of cliffs or the banks of raging rivers. The more you know, the better: