What's the second hidden partition on Windows 7?

I have asked myself this question since the beta release of Windows 7. This partition includes the so-called Windows Recovery Environment (Windows RE) and is also required for Bitlocker to integrate encrypted partitions (this requires a recovery key). The Windows RE is included in Windows Vista, Windows Server 2008 and now also in Windows 7. It can be started or installed from hard disk, optical media (for example the Windows installation DVD) or via PXE.

The Windows RE is used when starting the installed operating system is no longer possible. About the Windows RE you can:

Have errors corrected automatically that affect the Windows startup process,
restore the operating system from an earlier system restore point,
restore the entire computer over an image of the whole computer,
test the memory and
Open the input command line to get full access to the data to fix any errors.
The Windows RE can be started by pressing F8 shortly before the Windows loading screen and selecting the appropriate repair point.