Open all users startup folder in Windows 8

Using Run dialog (WinKey+r), type:

shell:common startup

or from the command line (cmd.exe) do:

explorer.exe shell:common startup

Reference(s):
http://www.winhelponline.com/blog/shell-commands-to-access-the-special-folders/
http://www.osattack.com/windows-7/huge-list-of-windows-7-shell-commands/
http://support.microsoft.com/kb/2806079