From what I know of bird flu, it's no more infectous than any other case of influenza.
http://en.wikipedia.org/wiki/InfluenzaIf memory serves the 3 most common ways of catching flu are your mouth, nose and eyes BUT (also if memory serves) 90% of infections happen because of contact between your hands and those parts of your body...not the air. If the only purpose the mask serves is to keep my finger out of my nose, then I'm that much safer LOL.
I've heard that Japan is one of the countries least at risk for a viral pandemic because of how few people shake hands and because they're very ritual about children washing their hands in school.