Seriously though, it is a fun if somewhat pricey hobby to get into. There is an active community at cocoontech.com and a number of hardware and/or software platforms you can choose from.
I have a setup deployed using CQC (CharmedQuark.com) as the software backbone which is very extensible and robust, though the marketing material isn't great. The online community there is small but vibrant (and some would say zealous).
If you have a significant other in the home then a key factor quickly becomes the reliability of any system that you wire into normal use. They won't be impressed if the bathroom lights don't work in the middle of the night ...
I'd recommend looking at Z-wave thermostats and the various 1-wire temperature probes. I've used the kits from http://www.midondesign.com successfully for these.
I had a friend in high school whose dad had set up an elaborate home automation system with simple 2-3 word voice controls for things like "turn on AC" or "turn on sprinklers". Anyway, this system was flawless until my friend's pet parrot Larry learned a few of these commands. One of the funnier situations was when the bird turned on the sprinklers during a dinner party!