I bought this in November 2010 because of the pretty bad battery life of the iphone 4 on its own. The Mophie is well packaged and fits the phone like a glove with a removable upper section to allow the phone to slide in. It has a nice 'feel' to it and does not make the 'phone too big and bulky. Charging the unit is via a micro USB connection on the side and this is where the problems start! I use the Mophie permanently i.e. I do not use the 'phone without it.
The socket for the USB connector is set into a plastic 'trim'at the bootom right hand side of the case. The trim appears to be very thin around the edge of the socket. What has happened in the last 5 months that I have had the phone case and with the regular connection and disconnection of a USB lead into it's socket is that the trim has snapped around the USB socket and is coming away from the case in its entirety!
So, I would ask people before buying this to think carefully as to how many times they are going to use the Mophie. If it's just as a backup for holidays etc then fine. But, if you want to use it as a permanent attachement to the phone with at least daily connection and re-connection of the USB lead then think twice before buying!