Although Windows 7 M3 build already contained a new boot screen which shows "Starting Windows..." text along with a glassy progressbar in the middle, the latest build "6954" is reported to have a brand new boot screen.
The latest Windows 7 build "6954" contains a new boot screen which shows animated items/balls that come together to form Windows logo.
Its not clear whether the same boot screen will be present in the RTM version or not. Also there are speculations that this new boot screen was also present in the previous Windows 7 builds but Microsoft kept it hidden just like they did with the taskbar.
One more interesting news is coming that Microsoft is planning to allow OEMs to have their own customized boot screens in Windows 7 which was not possible in Windows Vista.
At the moment we can only wait for the next build...