I'm a hospital nurse in Canada, and this is what our infection control departments/courses teach about masks:

The N-95 (AKA respirator) mask is for situations that require airborne precautions, and the normal facemasks are for situations that require droplet precautions.

THe N-95s form a tight seal around the face, and you breathe air through a filter that prevents the passage of microbes. Airborne precautions are for the few diseases that are spread through the air... most notably TB and chickenpox... these germs can basically float around in the air for as long as they're viable. In the hospital, patients with TB or chickenpox should be put into negative pressure rooms, so that when you open the door, hallway air is sucked into the patient room, rather than the patient room air being able to drift into the hallway.

Facemasks, on the other hand, fit loosely over the nose and nose, and you breathe the air leaking around them with no filtering. They are used to control diseases that are spread by droplets - i.e., the germs are on little drops of water that you sneeze or cough out, are propelled a couple of metres out then fall harmlessly to the ground (unless they hit a face, subway pole, etc. that's in range). Facemasks are the standard of care for patients with most respiratory diseases (including flu), or for any patient interaction where you might get bodily fluids splashed up on you (i.e. suctioning), or where you don't want your own coughs or sneezes to hit the patient or sterile equipment. They can also optionally be used for diseases that are spread by contact rather than droplets (i.e. MRSA, diarrheal infections) to prevent yourself from absentmindedly touching your face with contaminated gloves.

So... why is the CDC recommending that swine flu patients be handled with N-95 masks, when flus are droplet-spread diseases normally handled with facemasks? I think it's because of the amount of uncertainty and alarm that surrounds the swine flu right now... they're going above and beyond standard precautions.

For a droplet-spread illness, the N-95 does offer a tiny bit more protection because it's airtight... for example, if somebody sneezed on you at close range and at just the right angle, they might be able to get a droplet past your facemask. Also, if you aren't using the facemask properly (i.e., not covering your nose, or keeping it on when it's wet so germs can travel through it) then it won't protect you from droplets. But, it should be kept in perspective that facemasks are the standard precaution used to prevent flu transmission, so don't panic if you can't get your hands on N-95s if the swine flu becomes more prevalent. Think of it this way... a facemask might provide 95% protection from the droplets you're exposed to, and the N-95 another 4% (I am thinking here only of the protection that masking can offer, not comparing them to the protection offered by handwashing and social distancing). Another thing to consider is that in the operating room, the surgeon is wearing a facemask, not an N-95 (unless the patient happens to have TB or chickenpox).

Also, you can make your own facemasks if you can't find them... tie a bandanna or dish towel around your face, and you're good to go. Just make sure that your nose and mouth are covered, that you change it if it's wet, and that you don't startle any bank security guards. The purpose of the facemask is to block sneezes/coughs and to keep your hands off your mouth... if you use your own ingenuity to figure out how to accomplish those goals, you will decrease your chances of getting the flu.