Stylish is your friend. I check every day or so to see if it's still there. When it goes I'll turn the style off.

@namespace url(http://www.w3.org/1999/xhtml);

@-moz-document domain("serverfault.com") {
#system-message { display : none ;}
}

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.