Not to be sensationalist, but this could be exceptionally bad.
This is a good catch-up of recent events. Most worrisome is the genetic analysis of the H5N1 strain found in birds in Vietnam that shows mutations progressing toward giving the virus the ability to survive and thrive in mammals. That's not the same as being able to reproduce freely in humans, but it's bad enough.
This abstract shows that the H5N1 series of viruses is exceptionally good at causing a cytokine and chemokine response in epithelial cells. Translating from the original Geek for the nonmedical readers, that means that infection by this virus makes the cells that line your respiratory system scream like an '80s hair band singer, and your immune system comes a-runnin' when those signals are sent, bringing with them a cellular beat-down on any infected cells, as well as a lot of extra water. Water is good, except when you're supposed to be breathing air and the water is where the air is supposed to be. That's the lethal pathogenesis of influenza -- it gives you a wicked viral pneumonia, and in an effort to kill the viruses your immune system tears your lungs apart. It's a condition called Adult Respiratory Distress Syndrome, or ARDS, and besides trying to kill you the efforts paradoxically make it more likely that you'll develop a bacterial pneumonia, because the lining of your bronchi (breathing tubes deep in your lungs) are supposed to eject the mucus and other gunk that builds up in your lungs. That doesn't happen so good when your lungs are getting a Malachi Crunch from the virus and your own immune system's efforts to get rid of the virus, and without the ejection the bacteria have the opportunity to set up shop and start causing trouble of their own.
Also paradoxically, "normal" influenza tends to kill the very old and the very young, people whose immune systems can't deal well with the viral onslaught that causes most of us to miss a week of work and then go on about our business. The 1918-9 epidemic of influenza killed primarily those with extremely strong immune systems, the majority of fatalities were in the 20-40 age range. This is probably because a strong immune system overreacts more strongly to this type of virus, causing even more ARDS.
A few questions you may be having about H5N1:
I've had the flu before. Am I immune to this one?
Almost assuredly not. Humans haven't seen H5N1 before, therefore we're starting from scratch at developing antibodies to it. A few people in the population may be immune through an immunological freak of nature, but 99.99%+ of people WILL get the virus if exposed to it.
I get the flu shot. Doesn't that help?
No. The flu shot is formulated depending on what current influenza is expected to be, not on H5N1. No flu shots today contain any assistance for dealing with H5N1. Flu shots give you fragments of viral protein, dead viruses or live but very weak viruses to act as a tackling dummy for your immune system, and when the real virus shows up your body knows what to do.
So they're going to have an H5N1 flu shot at SOME point right?
Right. The problem is that we don't know precisely what the virus will "look" like at an immunological level when it gets to humans, so we can't really hit a moving target. There is an experimental virus for the bird-type H5N1 that rarely infects people, but that may not be overly useful when the Big One hits the human population. Expect six months to a year AFTER the virus hits to see a vaccine...which unfortunately means we have to live with the virus for six to twelve months, and treat it rather than prevent it.
What does H5N1 mean, anyway?
H and N refer to two proteins in the influenza virus, hemagglutinin and neuranimidase. There are variations in the H and N proteins, the H5N1 variant has H type 5 and N type 1. No human influenza virus has ever shown this type of combination, and so the immune system is unaware of its existance. The rare person that is immune to it probably developed antibodies that will bind to the virus "by accident" during a previous infection. Most everyone has no immunity to this virus.
So if I get sick, do I get Tamiflu?
If you can find it. The first people to get H5N1 will look like they have normal flu until they get much, much sicker than everyone else. H5N1 will be circulating with all the other normal influenza viruses, if H5N1 hits during a normal flu season it will be hard to tell except that all of the sudden your hospital starts filling up with pneumonia patients. Tamiflu is in short supply now, and the ability to crank it out in large amounts is limited by the feed stock for the drug, which believe it or not is the seed pods from the Chinese Star Anise plant. Already 90% of Chinese Star Anise production is bought by Roche for use in making Tamiflu. There are other ways to get the starting molecule (called shikimic acid, if you care), but at this point nobody in the world can snap their fingers and have Tamiflu appear in mass quantities.
Gee, this sounds like a big poop sandwich!
Indeed. A few more mutations and things will get very bad, very quick. No matter where you are, you're only about 48 hours from any other point in the Earth these days. The hope is that the outbreak will begin in some remote area where nobody other than the WHO goes, we can build a giant fence and quarantine the place, hose it down with Tamiflu and get a sample of the virus back to the lab to make a vaccine. That is somewhat unlikely to happen. If the wildtype virus appears in a big city like Jakarta or Shanghai or Beijing, it will begin spreading along the commerce routes back to the US and everywhere else in the world. SARS was much harder to catch than influenza, and it made it all the way to Canada within a couple of months.
The risk of influenza is not that you personally will die -- even the killer 1918 flu only had a 2% mortality rate, before ICUs and antibiotics. The risk is our fear of each other, and the fear of gathering in big bunches. School will be out for the duration in affected areas, and even something like shopping will become a potentially dangerous undertaking. All those people in Japan that wear masks will look prescient instead of goofy, and hand sanitizer companies will make a FORTUNE.
My advice -- have some extra food on hand. Have an extra bottle or two of hand sanitizer, don't touch your eyes (easy to spread viruses that way) and pay attention to the news. I don't think this is an "if" thing anymore, this is a "when".
Oh, and read The Great Influenza by John Barry. Superb book. Our society is much better able to handle something like this from a medical standpoint than it was in 1918, but it won't be a peach. And when it does happen, don't act a fool.