We already know a bit about Google's automated wiretap system for Gmail, because it was the system that the Chinese attacked in 2009/2010 in an attempt to access the accounts of Tibetan human right's campaigners.[1][2]
Bruce Schneier wrote a bit about this back in 2010[3]
I'm surprised no one has mentioned this before, since it's public confirmation of much of what the PRISM documents say, on the record.
[1] http://www.washingtonpost.com/world/national-security/chines...
[2] http://www.techcentral.ie/21618/aurora-hackers-may-have-acce...
[3] http://edition.cnn.com/2010/OPINION/01/23/schneier.google.ha...