Make no mistake - it IS very serious. They are right for being prepared. If (most say when) the virus evolves, those that do not die will still be very, very sick which means that most of the working world will shut down.
It's like this. People as a population build immunity to the various bugs and viruses we come in contact with daily because they are "common". The H5N1 is not common. It's only been experienced by a very small amount of the population, mostly those in rural areas with direct contact with birds and a lack of safety or quality controls. 60%+ of people infected die. So if (when) it evolves, it will spread rapidly and infect people with extreme severity while our bodies shit themselves trying to fight it off. Those less fortunate souls with weak immune systems (children, old people, etc.) will die in droves. The rest of us will die too, but not in as great of numbers. We'll just be fucking frighteningly sick for weeks.
Let's hope if (when) it evolves, it doesn't get transferred through the air. If it's only direct contact transmittable, it will help the situation significantly. Having a girlfriend who works for the health department can be very unnerving. You would be afraid if you've heard some of things I have and how they are "preparing" for this...