Ironically enough, I have ran across two sites this week (one that I did and one that I did not do) running 1.6.7 that all of a sudden have no styles in the control panel. This is how the source code looks:
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Login | ExpressionEngine</title>
<meta http-equiv='content-type' content='text/html; charset=utf-8' >
<meta http-equiv='expires' content='-1' >
<meta http-equiv='expires' content='Mon, 01 Jan 1970 23:59:59 GMT' >
<meta http-equiv='pragma' content='no-cache' >
<style type='text/css'>
</style>
...Every page of the control panel is missing this style information. I figured an update to 1.6.9 would probably solve it, but I would like to know why it happened and if there is a quicker fix than updating.