Our testing was performed in and around the Las Vegas area (CTIA!) with the net result of an average 25 dB gain on our testing unit. In the example photos, without the iBooster we had a -87dBm signal strength and with the iBooster a -61dBm signal strength.
The iBooster cradle unit in addition to offering a substantial signal boost also charges the iPhone. The auxiliary port located on the bottom of the iBooster is a duplication of the iPhone port giving further functionality for added accessories that require the bottom connection.
On a CTIA side note, the HTC Touch Diamond2 is *so* cool!