Mister is an open source home automation program. It's fun, it's free, and it's entirely geeky. Written in Perl, it fires events based on time, web, socket, voice, and serial data. It currently runs on Windows 95/98/NT/2k/XP and on most Unix based platforms, including Linux and Mac OSX.
I've had exceptional luck using SpamAssassin to block all of the X10 spam.
In other realms, I've used Perl and X10 gadgets to turn lamps and plasma ball on and off throughout the domicile...I always figured there would be more interesting uses.