static bool IsUserStale(User user)
{
//ignore tagged objects
if (user.Tag == tag) return false;
//ignore user with metadata
if (user.CheckExistingMetaData() != null) return false;
//ignore user with a last modification within last day
//TODO: hardcoded as one day, consider making configurable
if ((user.Left != DateTime.MinValue) && ((DateTime.UtcNow - user.LastChanged).TotalDays <= 1.0)) return false;
//user data is stale
return true;
}