A couple of links in my book (out of 1400+) managed to get past my process for checking and validating them. Pages numbers are in the PDF:

• Page 263: Second paragraph under "CSS 2D and 3D Transforms", the link to http://www.w3.org/TR/css3-3d-transforms/ has an extra space after http:// making it invalid.
• Page 529, last paragraph on page,  WebUIProtocolActivatedEventArgs has two URIs in it so it's an invalid link. The correct URI is http://msdn.microsoft.com/library/windows/apps/windows.ui.webui.webuiprotocolactivatedeventargs.aspx.
• Page 553, in "Contact Picker Providers" section, first paragraph under code snippet, the link for ContactPickerUI has extra (invalid) text in the URI. The correct URI is http://msdn.microsoft.com/library/windows/apps/windows.applicationmodel.contacts.provider.contactpickerui.aspx.

For checking links, I found a very helpful add-in for Microsoft Word (2010…now waiting for one that works with Office 2013!) from ablebits.com. See http://www.ablebits.com/word-links-manager/index.php for details. The product as a 15-day free trial, and a license costs $9.95. This was well worth it for how much time it saved me in the last weeks of production!