Comment by guelo

About the "quite literally can watch your ideas form as you type" quote, it's not clear that it's referring to PRISM. It came at the end of the long WaPo article and comes across to me as something Snowden might have said about NSA's capabilities in general, not necessarily PRISM.

  Firsthand experience with these systems, and horror at their capabilities, 
  is what drove a career intelligence officer to provide PowerPoint slides 
  about PRISM and supporting materials to The Washington Post in order to 
  expose what he believes to be a gross intrusion on privacy. “They quite 
  literally can watch your ideas form as you type,” the officer said.

If the NSA is snooping at the line level, which we know since the AT&T closet revelation a decade ago that they do, then they could see real-time typing in apps like Google Instant.