UPDATE: With the release version of OS X Mavericks there is now a much easier way to create a bootable installer. Simply follow these steps.
1) Download Mavericks from the Mac App Store but do not click install. If you install then after it upgrades your machine the installer will be automatically deleted.
2) Insert a USB flash drive and use Disk Utility to format it, name it ‘Untitled’. The installer takes over 4GB so you’ll need at least an 8GB drive.
3) Open terminal and run the following command…
sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ OS\ X\ Mavericks.app --nointeraction
4) You’ll see some output in Terminal letting you know it’s copying files. When that’s done your USB will be ready with the bootable installer.