I use an Ursack (plus OP sack) too, Sarah, because I can't throw (arthritis and lack of skill) and therefore can't hang my food. However, even though I have used it there (shhh!), the Ursack is not a legal method of food storage in Wyoming's Wind Rivers. I won't recommend it for use there for that reason.
Actually, my Bearikade Weekender (bought for the Olympic NP coast) is also illegal in the Winds, because California-centric Wild Ideas has never tried to get approval from the IGBC (Interagency Grizzly Bear Committee). So in the Winds I'm illegal no matter what I do!
On the other hand, the hanging method recommended in the previously mentioned Food Storage Order for the Winds is extremely simple for a bear to overcome (no counter balance, no PCT method, just throw the bag over a branch and tie the end of the rope to the tree trunk. For laughs (especially if you know Sierra bears), go to the Bridger Teton National Forest home page, click "Recreation" on the left, then click "Food Storage Requirements" on the right, then click "Food Storage Basics" and check the illustrations. (That's easier than trying to quote the yards-long URL on the new USFS websites.)
It's the folks who make no effort at securing their food from bears, rodents and other varmints that bother me. If a grizz comes after them in the night or a marmot chews a big hole in their tent, they deserve what they get, although the bear (which will end up being shot) doesn't. But the rest of us will have to cope with the aggressive backpacker-fed critters they leave in their wake!