Solar Powered Chargers

In light of the recent disaster in Japan this is a good time to think about how we use energy in our daily lives. I am wondering about the capacity of solar powered chargers for iPhones and iPads. Do they work well, hold a charge, easy to use? Let me know if you have any of these answers or experience with these type of chargers. Maybe we should be able to use the sun to power up our electronic devices.