You may want to check out One Wire Weather, http://oww.sourceforge.net/. It is a Linux based weather station that can run on the Pi. I plan to move my installation from a 13 year old Dell desktop to the Pi when I have some time.
As far as the OpenSprinkler Pi doing more than controlling irrigation, I think it can do a lot more then checking the clock for something to do. I have one running in production and another as a test bed. The test bed is running Dan’s program and acts as an Xbee to Ethernet gateway so my Vera Lite can talk to my XBee/Teensy LED light controller. Seems to work fine so far.