Windows live sign in assistant is a internet explorer plugin and Active X component that let you display multiple hotmail user accounts on the login screen at the same time, recreating the experience we got with Windows XP on hotmail website.
The best feature of the program is that it will get the account info automatically from windows live messenger, that means that if you got window live signing assistance installed on the computer and add another hotmail account to your windows live messenger, using the "remember this email address" and "remember my password" feature will automatically add that account to Windows hotmail logon screen.
In the past we had to switch accounts and input password each time we wanted to check our second hotmail account or if your parents wanted to check theirs. Sometimes they were prompted to type your password due to system cookies; now with windows live signing assistant your credentials are store on your computer, so there wont be any privace issue because it wont be used on public computers and your credentials are encrypted to your user account.
Just don't use them on another user account!