When I lived in China in 2002, we had more than a few dust storms where the sky would turn completely yellow...it is a bizarre surreal experience.
On my recent tour of duty starting in late 2007, I only experienced one dust storm in the spring of 2008, then nothing. I haven't seen one for a very long time, but it could be that they've just solved the problem for Beijing (doubtful, since we are right smack next to Inner Mongolia).
This is like the only thing...the only thing...that has gotten better in China while I've been here!