If you’re a Mac user, your OS X volume is likely your default volume. That means when you reboot from Windows, you’ll automatically boot back into OS X. If you’d like to reboot back into Windows (say, if you’re rebooting because you had to install some $%@ Windows updates), just open up Notepad and paste the code below:
c:progra~1Bootca~1bootcamp.exe -StartupDisk “Windows”
Shutdown /r /t 0
Where Windows is the name of your OS X startup volume. Save the file with a .bat extension (mine’s called “Reboot Into OS X.bat”) wherever you’d like. When you double-click on it, your computer will reboot right back into Windows, no Option key required.