Other than the crappy reception I get on my iPhone, one of my biggest issues with it is its non-removable battery. Coming from a BlackBerry--for which I carried a spare battery--this was a tough compromise. To make up for it, I have a Macsense JustMoblie Gum Pro portable power unit, and it's very nice, allowing me to keep the iPhone charged--in fact, colleagues and friends occasionally ask to plug into my Gum Pro to give their iPhones a quick hit.
The ZAGGsparq is something I received an e-mail announcement for (having been a ZAGG customer in the past), but at $129.99, I decided to pass. The reason I wanted one is because it plugs directly into the wall (no cable needed to charge it), and it has more juice than a Gum Pro (6000 mAh versus the Gum Pro's 4400 mAh), which I think is the equivalent of four full iPhone charges versus around three. Also, whereas the Gum Pro requires a mini-USB cable to plug it into the wall to charge it, the ZAGGsparq has its wall prongs built right in, so plugs into the wall without a cable.
I just received an e-mail tonight that it's on sale for $69.99, so I couldn't resist at that price and ordered one. I think it's going to remain that price only through Christmas (but I don't think you can have it shipped to arrive in time for Christmas now).
If you're an iPhone user who travels and/or talks a lot, something like the Gum Pro or the ZAGGsparq is, in my opinion, an absolute must. I haven't received my ZAGGsparq yet, but it looks pretty cool, especially at $69.99, which is about what the Gum Pro is priced at. (I use the Gum Pro to charge several of my devices that charge via USB, and will do the same with the ZAGGsparq.)