PeterB said: so far there is no reason to suppose it will turn really nasty
I went to a forum a couple of weeks ago for Health staff at the hospital. The Director of Infectious Diseases gave a long, full of medical jargon, presentation about the Swine flu (H1N1 please) and about several pandemics since the renowned pandemic in 1918. There has been only one really truly serious one since then, with over a million dead (in the sixties if I recall correctly), but there were several other pandemics without high death rates. What they found is there is always a "second spike" often when it comes back in the summer. I think this is the fear behind the swine flu - it is changing all the time.
Additionally, they are fearing, sooner or later, this year, this decade or sometime in the future, that there will be a repeat of 1918.