Notebooks and Mini ITX Machines as Home Servers?

An anonymous reader asks: "I recently moved into a townhouse (the first time on my own, actually) and need to get a server up and running before the other trivial stuff (furniture, getting food in the fridge, *getting* a fridge, etc, etc). I need the basic set of services - HTTP, FTP, DNS, SMTP/POP3 for any self respecting geek. The drawback is that I'm on a limited budget (money and space wise) and need a server that is *extremely* energy efficient, takes up little space, makes no noise, and generates very little heat. A basic P4 notebook seems to fit the bill - small, low power consumption, built in screen/keyboard/mouse (no need for KVM), wireless so I can stick it on the top shelf of my closet, and generates less heat and noise than your average desktop. Is there any reason to consider, say, a mini ITX rig (such as a shuttle) over this? Any drawbacks?"