ASUS has a new feature called Express Gate that can boot a PC in about 5 seconds. It's a special version of Linux embedded on the motherboard. It's designed to start fast, but it's limited to basic tasks. You can still start the PC into Windows when you want. In addition to being available on some ASUS PCs, it's available on a small number of models from Lenovo (called Quick Start), LG (called Smart-On), Acer, HP and Sony. 

One situation where this might work out well is if there is a family member that you don't want using Windows. You should be able to set up Windows so that it requires a password, but the other person could check their email, etc. with Express Gate.