I have used a power monkey explorer for about a year now, and it gets used at least once per week. If anyone is looking to get a recharging system, then it is worth considering if you want to carry it with you, or whether it will be in the car. Also, remember what devices you wish to charge (I know that sounds obvious lol).
If you are keeping your charger in the car, then a spare/leisure battery will have the most power on tap, and will be able to run laptops (via inverter), charge phones, PDA's small consoles, and run lighting or DVD players etc.
Provided you are with the vehicle, then an inverter will do similar.
Back to power monkey's. If you have an Iphone, then something like a power monkey is ideal, as other well known chargers will often not have the power to charge an Iphone (especially the 3Gs onwards!), and can only manage ordinary mobiles (which is why some of their ads only mention Ipods, rather than Iphones).
To use my power monkey, I would completely charge it before the journey (car charger, PC, mains UK or mains worldwide), and then once out in the field, I will often even leave the solar monkey on the top of my tent during the day to keep charging the power monkey, or I will attach them to the top of my rucksack as I am walking along. During an average summer day (as in daylight time, and not just sun) I can charge my Iphone (or three mobiles, as the power monkey comes with adaptoer for most companies, as well as for small consoles etc)) in the morning, and then during the day, charge my sisters' and her boyfriend's mobiles. After that the solar monkey is often used to run a small games console for an hour or two, and then in the evening it goes back on the tent to fully recharge the power monkey again (so we can watch a film etc on the Iphone during the night). It will continue to charge until around twenty minutes after the sun has gone below the skyline, which shows that it does not need direct sunlight.
When not in use, the power monkey will hold its charge well for over three months, and will still completely charge one Iphone or about three ordinary mobiles.
There is another device I use called the solar nut, which has a tiny reserve battery, that allows the power monkey to continue to charge for short periods, even in complete darkness. This can be useful for cycling (with random tunnels) or for very overcast days. The solar nut is not as useful as the power monkey/solar combo IMHO
So, for Iphones, I think the power monkey is one of the best chargers on the market, if you want a durable, small, light and easy to use system. For ordinary mobiles, the choice widens, but it would be worth noting that as the power monkey could easily charge 7-8 mobiles per day, it can be a good group buy.
As with all of my 'essential' electricals, I bought the power monkey in yellow, and then added yellow reflective tape (for easy finding if dropped in the dark).
Just my experience of a years use
Edited to add: If you are on a longer trip (or have a charger that only charges from USB, and forgot to charge it lol), and want to re charge your charger in some friendly persons home, get yourself a USB/mains adapter plug, as it would be 'pushing it' to ask anyone if you can connect a USB plug to their PC (and frankly, stupid of them to let you, in these days of identity theft). I have never needed to use this system while out backpacking (as solar has always solved the problem, even for a weeks travel), but have used mains charging while on business trips.
