But last time I upgraded my computer I switched to micro ATX and I'm happier with that size. Any maintenance or upgrades are a breeze with room to get your fingers around the components, I didn't need to buy a special low profile CPU cooler, it's small enough, and if I need an extra PCIe slot for something I've got it.
The new computer is mounted it to under my desk where it's out of the way. Unless you're carrying your desktop around to LAN parties I think this is an overall nicer solution to "desktops take up space" than tiny form factor cases.