When i enable Page Cache (with apc) strange things happen.
Lets say im logged in with admin user Jim using FF. In WP 3.1 i see the admin panel with my name on the header, now i open chrome (delete all cache & cookies ) and i continue to see the admin panel, of course if i click on "Dashboard" it asks to log in. Also if i click a comment link (http://domain.com/post#comment23) the comment-form says "Logged in as $Name_of_last_user_left_a_comment". I had these problems with 3.0 also.
How to fix this?