A home controlled by the PC (hopefully better looking than the current version).
Wireless connections controlling the heating via sensors to detect occupancy, usage and temperature needs for each room independant of the rest of the house.
Water systems controlled for maximum efficiency and minimum usage.
Lighting and security all controlled from anywhere via the internet.
And, of course, home entertainment, TV, video (via the HDD), music and DVD's all controlled by and provided through the PC.
Oh, and finally (for the genius amonst us), a replacement for the door key - why can I get into my car without fumbling with the lock but I get soaked while opening the front door?