I fully agree with the "test before you go" advice - I usually fill all the bottles I'm taking the night before I go, and leave them standing in a bowl so I can check for leaks the next morning.

I know there was an issue with the earlier version of the Sawyer bags (the ones that came out with the first release of the filter.) They supposedly fixed it with this year's models. I never had any problem with the originals (but only used them a couple of times), but I ordered a set of the new ones this year and, so far, no issues with them, either (maybe 4 weekend uses, so far.) For what it's worth, I also grabbed a few of the Evernew bottles, just in case, so at the first sign of trouble...