I was, granted, having some login issues before I upgraded, which I think I just made worse, but I thought reinstalling WordPress would fix the problem, and if I was reinstalling, I might as well upgrade, right?
Well, I ran upgrade.php, and got a message that I had upgraded successfully, but now when I go to /wordpress/wp-admin/index.php, I get:
Invalid Header: [HTTP/1.1 302 Moved Temporarily]
Missing Content-Type Header!
HTTP/1.1 302 Moved Temporarily
Set-Cookie: bb2_screener_=1181337955+126.96.36.199; path=/blog/
Expires: Wed, 11 Jan 1984 05:00:00 GMT
Last-Modified: Fri, 08 Jun 2007 21:25:55 GMT
Cache-Control: no-cache, must-revalidate, max-age=0
Location: [my site]/wordpress/wp-login.php?redirect_to=%2Fwordpress%2Fwp-admin%2Findex.php