Google’s indexing often seems to stretch into the most obscure corners of the net, but there are plenty of sites it deliberately doesn’t index, even within its own domains. Google Operating System runs down some of the more interesting areas of Google that don’t get indexed. It’s no surprise that search results pages, mobile replicas of pages and Google Documents are kept private, but some of the other exceptions (like image pages only being available via image search, video captions being ignored, or Google Moderator not being indexed) seem more questionable.