I picked up a Solio about 9 months ago; had a gift card burning a hole in my pocket. I haven't done extensive field testing with it, but I used it enough to get a feel for what it needs to function.

It does require pretty direct sunlight to do anything; in less than optimal conditions it will likely take more than a day's sunlight to fully charge from empty. However, I have the internal battery fully charged up from my computer's USB port and after the last 8 months of just sitting around it is still showing 80-100% charge. The main benefit in my mind was the USB connector; since just about every device I would want to charge from this (sadly, netbooks and other laptops are too much for it) has a USB cable, I can rely on this to keep our cell phones, GPS, and even my wife's Kindle viable in a short-term emergency. In the long-term or on an extended backwoods trip it will provide enough juice to keep our com gear running. I even have a AA/AAA charger that runs from a USB port and so is covered if need be.