In this day of age, it's very practical to have a Windows 7 installation on your USB key, for many netbooks and devices don't come with CD/DVD drives anymore.
Windows 7 have a nifty feature which combines the windows of opened applications under the same taskbar button. If you don't like it you can always turn it off.
Some installations or settings changes require you to restart your computer. In most cases you don't need to actually reboot it, you only need to restart the explorer.exe process.