We've squeezed an implementation of SFW into the confines of an Arduino. It talks to the world in json through an ethernet shield.
Arduino Diecimila with Atmel 8-Bit AVR Microcontroller
We deployed a battery powered server in a Community Garden where it monitored soil signals for most of a year.
See Remote Sensing with Federated Wiki for engineering details of the deployment.
See Agave Research Project for a similar soil temperature study in Phoenix, Arizona.