Maybe it's incorrect, but I've read these are not particularly effective. They work great if the person who is sick wears it, but if you wear it they are far less effective.

Put another way, it sounds like generally they are more effective at keeping germs in than out. Hopefully that's wrong, if it is, I'll consider this in the future. More and more flights seem to be filled with sickies. And who can blame folks, with change fees what they are these days, no one is going to change their plans unless they are about to keel over.