Stylish is your friend if using Firefox.
@namespace url(http://www.w3.org/1999/xhtml);
@-moz-document domain("serverfault.com") {
#system-message { display : none ;}
}
Stylist is your friend if using Chrome.
Prefix http://serverfault.com
rule
#system-message {display : none ;}
I check every day or so to see if it's still there. When it goes I'll turn the style off.