My daughter has a medical condition that requires me to be able to stay in touch, so this is a hot button issue for me. I had the Goal Zero as well and it was fine during perfect conditions, but it just didn't seem to keep up when actually hiking or in low light. Sold it and got a Joos Orange which is AMAZING. It's the only solar charger I have used that has got the job done tied to my pack, but it weighs 24 ounces, so it limits where I'll carry it.
Ultimately, I went with two Anker 5600 mAh external batteries usb charger. They weigh 3.9 ounces each and only cost $35. My Droid Bionic has a 1500 mAh battery, so I'll take one for 1-4 days trips and two for trips up to or over a week long. The two combined has enough juice for 7.5 complete charges and you'll be hard pressed to find that kind of power in something under 8 ounces and RELIABLE. They are also much smaller than than the New Trent batteries, so they are more packable.
Also, I always keep one in my wife's purse, so we have backup power anywhere. I can't say enough good things about it.