One of our family friends came over tonight complaining of her cursor going missing after applying the Windows 8.1 upgrade to her new laptop. After a lot of fussing with it for 20 minutes and some google-fu I found this thread:

http://answers.microsoft.com/en-us/windows/forum/windows_8-tms/windows-8-mouse-pointer-disappeared/0814da98-0e28-4a3c-b0a1-8125440eacab

Which explains that for whatever reason toggling the trackpad disable button causes the cursor to re-appear and stay visible even when re-disabling it. Quite an irritating bug.