Are bees disappearing and why? According to the web site of the film Vanishing of the Bees: > Bees are dying in their billions. In the UK, around one fifth of honeybee hives were lost in the winter of 2008/2009. Is there evidence of bees disappearing and what are scientific theories on this subject?

I would hesitate to say that "bees are disappearing". But yes, there is a problem.
It's called Colony Collapse Disorder and there is nothing certain about why it happens. It's probably a combination of factors. The Wikipedia article is good. I've recently read some articles claiming that they have found a definitive link to some disease, but I can't find it right now, so I don't know if there is any good basis for the claim.

Update: The claims blaming the pesticide Imidacloprid seems promising and seem to be the strongest claims of a cause at the moment.