So last week I tried attaching one of YwRobot's soil conductivity meters (good proxy for soil moisture) to the MultispeQ device and PhotosynQ's data display / sharing / analysis backend.
It worked great! See the full blog post for details.
Next, I really want to try to connect another public lab's sensor and do some more detailed analysis using the online analysis tool, I'm going to try the riffle (or at least a riffle arduino sketch on a Arduino Uno board). If you have other arduino compatible devices to try to connect let me know.