For those people who aren't worrying too much about the 4% mortality rate, keep in mind:
Between the easy means of transmission, and the frequency of mutation, SARS has the properties which make the cold or the flu such common diseases. This means that, if it establishes it a similar foothold, it could be the same sort of recurring, everybody-gets-it-eventually diseases.
That's a very bad scenario, considering the 4% mortality rate (which is probably not an accurate number.) It's hard to estimate what percentage of the population gets infected any given year, but even if just .5% do, that's still about 60,000 new deaths in the US alone. I'm not sure what the annual death rate is for any given thing (car accidents, I'd imagine, are still higher), but that doesn't matter: Just because it isn't the end of the world, doesn't mean it isn't a significant change in the world. An extra 60,000 deaths is going to have repercussions on any economy and society...
Of course, that's what I'd call the worst-case scenario, or at least the worst one that's supported by the evidence. There's a reasonable chance of this If it becomes a regularity, and we can't find treatment for it, the annual worldwide death toll could easily reach into the millions. The big feature there is that it would be a regular phenomenon.
Now, one of the keys to this being a possibility is that very 4% mortality rate. One of the reasons ebola wasn't more devastating than it was was the high mortality rate: It would sweep through an area, and people would be gone before they could infect anyone else. SARS doesn't interrupt its own spread like that... It has a decent latency period, a high potential for transmission, and a relatively low mortality rate -- that's a recipe for epidemic.
Will it become an epidemic? No, or at least, not if it doesn't have any surprises left. The heavy-handed response by the WHO as well as various national health care administrations are probably the best approach -- if anything, they take the disease too seriously (compared to what the evidence suggests), but hey, "err on the side of caution." The news media, for what it's worth, is at least doing its part in getting the public sufficiently concerned (even if there approach seems stupid given the actual facts) -- if it gets people to wash their hands and cover their mouths when they cough, there's that much less potential for transmission. (Although I've heard more than a few debates about whether or not covering your mouth when you cough is a good social custom -- it results in a higher concentration of infectious agents on a smaller area, such as the next doorknob you touch, instead of letting them disperse into a less-concentrated and therefore less-infectious space... Of course, with something as infectious as SARS, it might be better to give it to the next guy who touches the doorknob rather than half the room you're in.)
