I've been through the typical publish/approve process and have, seemingly, successfully published a page (I've checked it's approval status in the manage content and structure section of the site which says approved. Does this mean it's published?).
However, when I run the following query (which does bring back the page in question), the PublishingStartDate is always empty:
//query.ViewFields = @"<FieldRef Name=""PublishingStartDate"" /><FieldRef Name=""Author"" />";