According to Dr. Sam Milham (author “Dirty Electricity”), there is more potential danger from the Smart Meters than the RF radiation.  Here is what he wrote in his letter to the CCST, January 2011:

My hypothesis is easy enough to test. Dirty electricity levels measured in homes, offices and schools should increase after the meters are deployed. Dirty electricity levels measured in the utility drops and in the earth will also increase as the meters are deployed. Since dirty electricity is a potent carcinogen (see attached paper and pp. 78-80 in my book), and causes numerous other health problems, the only way to avoid a public health catastrophe is to send the smart meter information over existing telephone land lines or go back to the analog meters. I’m not making light of or ignoring the RF pollution caused by the smart meters, but think the dirty electricity may be a more serious and intractable problem.

Also see this very helpful article from EON3EMFblog which explains Switching-Mode Power Supply.