If you find the minipwner project interesting, here are a few similar projects you might like to learn more about:
THe Pwnie Express was the first commercially available pen testing drop box. Its linux running on top of a SheevaPlug, and they've built some web-based scripts to automate the tasks of configuration and establishing connections. It is powerful enough to run packages like Metasploit on the box, but it doesn't have integrated wireless.
The F-Bomb is a recent project that we're just starting to hear about. Brendan O'Connor has built a custom case around a PogoPlug computer board, and it sounds like he's built in interfaces for various sensors and other expandability.
The Wifi Pineapple is comprised mainly of some wrapper scripts and interfaces around Karma running on a La Fonera or similar wireless router. The PineApple Mark IV is actually pretty awesome - similar specs to the MiniPwner but better antenna, 8M Flash onboard, and two NIC's. But you need to flash it via Serial connection to get started.
You can get a good deal on the Hornet router that the pineapple Mark IV uses at Http://jpgottech.com/tekshop . They have the 8M version...if you buy elsewhere be sure to get the 8M version (there's a 4M version of this same router).
I'm really excited to see these go into general availability. The Raspberry Pi is an inexpensive credit-card sized computer. It uses an external keyboard and RCA (TV Video) out for a display, and has interfaces for USB, SD Card, and Ethernet (on a more expensive model). There is also an expansion/prototyping board in the works called a GertBoard that will allow you to connect sensors, lights, motors, etc. and drive them from the RaspBerry Pi.