We see some odd differences (possibly just since the last release) in the "Administrative Permissions" section of the user profile for a Sites anonymous user (Setup > Develop > Sites > [your site] > Public Access Settings).
On NA14 (partner DE), my profile has the following options under "Administrative Permissions":
On EMEA (EE), my profile has a different set of options:
Specifically, the lack of a "View All Users" permission appears to be actually a lack of that permission entirely. This is causing issues as we have some Sites code that queries a User record.
This functionality was working at most a month ago, so we are scratching our heads as to what has changed (and why the difference between the orgs).
Was "View All Users" revoked in the latest release?