Just returned from Ride Idaho 2013, 400+ miles, six days, northern Idaho panhandle, 370 or so riders. Lots of solar panels this year. By far, the most popular device was the Goal Zero 7. I counted 12 of them in camp. The ham radio operators had 5 more at their fee-based charging station (along with a Honda generator and one of Goal Zero's huge survival-grade solar collectors). This model 7 produces enough power to directly push an iPhone but still requires a bulk storage system to push a tablet.
Why was this the most popular model? The answer I got from several folks: it's available at Costco in a package that is aggressively priced to move.
I took along my little GZ 3.5 and the 4-AA batt pack. The pack only moves the iphone battery charge indicator about 25% even when the pack is completely topped off. So if the phone drops below 70% or so, it will never come all the way back to 100%. Running without the GPS apps and powering down preserved the iPhone but it usually got below 50% by night time. The battery pack only pushed it back to 60-70% so I poached AC mains power couple of times.
I rode with the phone off most of the time but the ipHone was also my camera so that complicated things. Next time I'll take a separate camera, probably equipped with an Eye-fi card to upload directly to the iPhone via wifi.
Sheesh. I just reread that last statement. I just committed to a stupidly complex system.