1. http://www.nwfusion.com/weblogs/cool/archives/002526.html notes that your 802.11b card has been boosted to 200 milliwatts.
2. Your average cell phone tops out at about 600 milliwatts and has been in decline as advances are made.
Given that item 1 (WiFi) is not held to your head, this issue begins to fade quickly as power diminishes exponentially with distance. Already at 1/3 or less the power of a cell phone and not strapped to your head, the issue here is just for fun discussion and comparison.
Moving to cell phones, the issue is that the studies are often flawed as you read articles from http://www.google.com/search?&q=cell+phone+milliwatts
Bottomline? It's your choice, but remember that even your standard telephone emits EM fields as you talk on that device. Its odd to fixate on cell phones when other sources (like a 1000 Watt Microwave oven) can produce fairly strong fields of varying RF and EM.
Given the simple items above, you'll do more by using the cell phone less than fretting about WiFi.
I have read several sources on wireless connectivity and have not yet found any information on the hazards of such. Seeing as there have been stories about damage caused by cell phone usage, are the frequencies used in the Wi-Fi standard similarly harmful to the human body?