The Arduino Pro Mini is SparkFun's minimal design approach to Arduino.  It's essentially a 5v Arduino that runs an 16 MHz bootloader on a super small, super thin board.  There are no connectors attached - allowing you to add whatever connectors or wire you want without too much trouble.The goal of the Pro Mini isn't to replace the Arduino so much as bring the cost down for more advanced users.  The Arduino Uno is still the inimitable board but if you're comfortable working within voltage...