A Smart Lawn Sprinkler System?

An anonymous reader asks: "I'm about to install a sprinkler system for my lawn. There are lots of timers and computers out there to automate the watering of your lawn. However, before I go out and buy something, I wanted to know if there are any interesting open source projects for watering lawns. I've heard about smart sprinklers that get weather from the internet/satellite and water accordingly. What have other Slashdot readers done?"