There are two distinct “new” display control panels developed prior to the Longhorn reset. The first appeared in Milestone 3, and was removed in early Milestone 4. The second was present only in build 4093. Though both are created in the Avalon UI framework, it seems almost certain that the two efforts were not connected beyond their functionality and underlying technology.
In many Longhorn builds, there are issues with partitioning and formatting disks within the installer. Microsoft DiskPart is a utility included within the Windows Pre-installation Environment that allows you to partition disks from a command line interface.
One common problem faced by people installing Longhorn on modern hardware is the apparent inability to boot from USB drives. As optical media grows rarer, and more and more form factors ship without optical media drives, booting from a disc is not always an option. Fortunately, booting Longhorn through USB can be a surprisingly easy affair once you know what you’re doing.
The Longhorn Start page is a feature present in Milestone 3 and early Milestone 4 builds. The start page appears to be an early attempt at replacing the OOBE (Out-Of-Box Experience) that these builds carry over from Windows XP.