If you're a dual booter and you want a quick and easy way to reboot from OS X into Windows, this AppleScript coupled with the magic of Quicksilver will do so with just a few keystrokes.
While you could always hold Option as you reboot or change your startup disk from System Preferences, this method is by far the easiest way to reboot your Mac into Windows. Just open up AppleScript Editor and paste in the following code:
do shell script "bless -mount /Volumes/WINDOWS/ -legacy -setBoot -nextonly" with administrator privileges do shell script "shutdown -r now" with administrator privileges
(where WINDOWS is the name of your Windows drive). Save the AppleScript anywhere you want—I saved mine as "Reboot Into Windows.scpt" in my dedicated Scripts folder.
If you haven't already, you'll need to add your Scripts folder to Quicksilver's catalog. Open up Quicksilver's preferences and hit the Catalog tab, then hit the plus sign. Navigate to your Scripts folder and add it. Once you have, look to the dropdown on the right-hand side of the window and choose "Folder Contents". This will catalog all the scripts in that folder for launching with Quicksilver.
Now, you can just trigger Quicksilver, type "reboot" and your reboot script will pop up, rebooting you right into Windows. Alternatively, you can also give it a hotkey with Quicksilver's Triggers function (located in the Preferences), if you prefer. I even gave it a cool icon that I had lying around on my computer. Hit the link for more info on other ways to use Quicksilver with this script.
Note: Unfortunately, this trick doesn't work if you are using previously mentioned NTFS-3G to write to your Windows drive. If you disable NTFS-3G in System Preferences and reboot, this script will work. As such, if you want to use this trick, I'd recommend disabling NTFS-3G and only enabling it during sessions where you actually need to write to your Windows drive.