Are cellular phones and Wifi really harming your health? Or is it all just hooey?

I came across a blog today suggesting a relationship between cellular phones, Wifi, and deleterious health effects such as weakened immune systems and cancer.
However, when I tried to find more information on the subject, I found a complete dearth of credible sources supporting this notion. There are thousands of blogs and websites saying that the phones and towers are harmful, but they tend to be rants or suppositions — without citations or research. Is this just the paranoia of our modern age? Are these fears the same as our parents had about microwave ovens a generation ago? Or is there cause for alarm?
The most informative site I’ve found so far is at ehso.com.
But I’d really like to know if there is hard science supporting these concerns, and where to read it.