Google Reader logging me out

Has Google Reader (or Google Accounts in general) implemented a stricter timeout system for logins, does anyone know? I've been automatically logged out several times today with the above message cheerfully displayed when it never used to happen before.

I'm thinking it could be my newly cleaned out cookie whitelist for PermitCookies in Firefox, but just want to make sure. Could Buzz have anything at all to do with it perhaps? If they are timing out sessions earlier it could be beneficial for security but I tend to have Reader permanently open in a tab and I'd hate to have to re-login every hour or so.