Has anyone here used a portable solar charger in the field?

It would need to be light enough to carry in a backpack and able to power mostly a laptop.

I was looking at this model: http://www.amazon.com/Solar-Laptop-Charger-Portable-Power/dp/B002UK25R4/ref=sr_1_8?ie=UTF8&qid=1307853993&sr=8-8

But wanted to see if anyone here had used anything that worked particularly well in the field.

Thanks.