It works, with my 3G & 3GS. I'd say it carries enough power to recharge the iPhone and still have a bit more left over for future use.
But I've seen an iPhone charger that is rubberized and covers all the edges. That's the one I'd buy, given a do-over. Saw it in use, not for sale. I was incorrectly directed to buy it from AT&T or Apple. I'm sure this rubberized version will be much more expensive, though.