Wifi - probably too low a power, even in the 'near field' zone.
Cell phones (and 3G Kindles) transmit a peak of 4 watts (when on - they are a pulse transmission).
The stories about those devices that get publicized do not consider 'near field' effects.
As a rule of thumb, consider "near field" less than 10 wavelengths for this post.
The peak power pattern(s) in 'near field' radiation is extremely difficult to compute.
(Well, when I was in school, it was considered impossible, but time passes, etc. ...)
So holding an antenna radiating 4 watts peak less than two wave lengths from your brain should not become a habit.
Although it has for millions of people.
I guess all we can do is wait a few generations and count the number of brain fried individuals in the general population.
"near field" ::
http://www.antenna-theory.com/basics/fieldRegions.php