Very interesting.
I just got latest from WP SVN and Popularity Contest SVN on wp-plugins.org. I ran upgrade.php on my existing database - hit the site a few times - everything worked perfectly.
Then I dropped the database and did a clean install in a new database. For some reason, now that there is a clean install, my 'is_admin_page' function (which checks for the existance of the 'check_admin_referer' function) now returns true, causing the plugin not to record any views.
The is_admin function (added in 2.x I believe) seems to accomplish the same goal as my 'is_admin_page' function, so I've added a patch to use that if it's available.
What I really don't understand though, it how the database change (upgraded DB vs. clean 2.x DB) made any difference. Also, why 'check_admin_referer' is active on non-admin pages now is beyond me.
Anyway - new version checked in to wp-plugins.org.