Here is my humble donation for your community, so I will not feel like reading here for free )
I made short video about levels of electromagnetic radiation that Kindle 4 emits while connected to Wi-Fi network.
About readings of my measurement gadget - guys, who made this gadget, recommend levels of 1-10 uW/m2 (micro watts per square meter) for sleeping area.
I think that if you take something to read, then you do it in your not working time, when you want to rest, so such radiation level is preferable.
Conclusion is - set your wi-fi off and don't use it )
Wireless router will give you readings like 2000-5000 uW/m2, so its really unhealthy to have wireless router in your apartment. Same to DECT phones.
Well, all written above is my opinion and I don't want to discuss it here.
Everyone who wants to know more about the radiation problem invited to see site www.bioinitiative.org
and read BioInitiative Report.
Bottom line: Kindle 4 gives low levels of radiation (relatively to smartphones).
Here is a video: