A few years ago I put a Kill-A-Watt meter on my counter top water boiler and saw that it took about 50 watt hours to bring 4 cups of water to a boil, about half of what a microwave uses and 1/4 of what it takes to boil on the stove top.
Most water boilers that I see in stores are plastic, a few are stainless steel but they still have a plastic window down the side, mine is all stainless steel inside, even if the plastic is not a health issue it is still a weak point that could start to leak and make the kettle useless.
Hamilton Beach 40898 Cool-Touch 8-Cup Cordless Electric Kettle : Amazon.com : Kitchen & Dining
What got me thinking about this device that I use every day is yesterday I was at a friends house and they had the same kind of device only it was glass! the element was bonded to the glass bottom and the water only came in contact with glass, they loved it and said they used it every day.
The Capresso H20 Kettle - Beautiful Heat-Resistant Kettle With An Automatic Shut Off Feature | DavidsTea