As mentioned in this thread, I got around to doing a write up of my home monitoring system.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1246826892/0#0
Its not an 'howto' but does contain a lot of details which may give you some ideas for your own projects.
http://pluggy.is-a-geek.com/arduino/index.html
Questions, suggestions and criticisms welcome.......