In 2000/XP/Vista it was easy to set a wallpaper for the logon screen, either manually through tools like Logonstudio or simple registry changes by hand on prepared installation images or through custom group policies.
In Windows 7 all this works as usual, but the secondary (or any additional) monitor is just black. The mouse pointer is visible on it but no matter what settings I can't get the logon wallpaper to tile (or stretch or fill or whatever) over onto it.
This makes it hard to OEM/company brand the installation for multi-monitor users. More annoying is the fact that it looks officially supported to brand the logon wallpaper in Windows 7 - as it's made extremely easy... apart from this little catch. XP and Vista has no problem tiling or stretching the logon wallpaper over multiple monitors.