On the weekend i set up openHAB.
So far, it's a server that receives states of the things in my house, and lets my configure up groups (rooms), display the status within those groups and add actions (like light switches and colour pickers) to the groups.
So far i've hooked up the milights we bought from wifilights.co.nz. I've connected to our XBMC and our netatmo.
There's a framework for arduino - called "Souliss" - that should make placing a few sensors around the house easy enough, then hooking it up to openHAB.
The widgets for blinds are intriguing. I've only seen those in hotels so far, but auto opening the curtains each morning could be useful.
Maybe a webcam on the goldfish tank.