There's a lot of FUD about the UrSacks. The reality is pretty hard to dig up. So, I wanted to post something with the actual *facts*.
Jess recently found this:
This paints a rather strikingly different picture than UrSack's website:
It's a fascinating read, and if you're upset about where UrSack's are allowed I highly recommend reading it. This paints a very different picture though of why the few places that don't accept them don't.
For backpackers like Jess and myself, a very low failure rate is acceptable. We're usually far in the backcountry where bears are rarely problematic, only rarely camping in established campsites. So we rarely have issues with bears anyway.
Additionally, we've personally seen one of our Ursacks get chewed on, and seen 2 others that have been chewed on. All of these survived with no issue, though in one case their olive oil was punctured (annoying for sure, but they still had their food, and the bear didn't). Note that in both these cases bears could be scared off easily, which is not true everywhere.
I should add, I originally purchased an aluminum liner for my UrSack. It was so annoying that I never ever did actually use it. The only reason to use it is for the rare places that require it - which is basically none now.
Remember that the UrSack isn't just an alternative to canisters, it's also an alternative to sleeping on your food, or bear-bagging. If you're bad at throwing rocks, it can easily save an hour in the evening. If there are no good limbs around, or the bears there know about the PCT method, or you're not sufficiently skilled at bearbagging, or you're too lazy to bearbag in the first place, it still works well, and at about the same weight as the rope needed to bearbag.
For us, we use UrSacks instead of (or in bad bear country even in addition to) bearbagging. This is super handy in alpine areas as it also discourages chipmunks, mice and coons. For the rare cases where the UrSacks are disallowed, I own a crappy canister that I loan out to friends. You can also buy one of the super-light ones if you really care.
Pay your money, take your choice. But those are the facts. Have fun, be safe, and please don't feed the bears.