I'm not big into writing product reviews... and I hesitate to stray off topic in a Flex forum. Ok... here we go.

Shortly after purchasing an iPhone 3G I realized that the devices battery wasn't sufficient for my definition of 'typical use.' In my search for a solution I only had two criteria... for starters I didn't want my phone to look like a banana in my pocket (e.g. size of the solution had to be reasonable) and finally it should live up to its claim of battery extension. If it provided some protection for the phone - that would be a welcome bonus.
At the time, the 3G iPhone was so new that only one company offered a solution. I order the Juice Pack from Mophie and anxiously awaited its arrival. Delivery time was great - within a week it arrived.
I used it faithfully for several weeks and was satisfied with the added oomph - it wasn't overly huge and it did deliver on the juice. However, I found myself worrying more and more about scuffs and scrapes; the cover doesn't fully cover the upper portion of the iPhone. So... the thought of carrying it with me and using it to just juice up when needed did cross my mind but toting a man-bag around with it, another case, and a chapstick 24/7 didn't appeal. Also, I noticed that even light friction (in an out of my jacket pocket) was wearing the soft-touch finish off revealing the hard plastic underneath.
Back to Google!
I was lucky to run across a Gizmodo post about a new product by Incase which looked right on the money. The Incase store wasn't taking direct orders on that particular day but the Apple Store was... (mini-victory dance).
It's been over a month now and I'm really happy with the Power Slider. The case provides good body protection (I've added an invisibleSHIELD from ZAGG for the touch screen) and only needs to be recharged every two or three days. I'd like to add that the Power Slider's soft touch finish is exceptionally durable... short of throwing it in a rock tumbler it's in great shape.
Verdict? A first round KO - no do-overs. The Incase Power Slider wins.
Incase Power Slider - ROWR!
Mophie Juice Pack - meh...