In addition to The Shadow Factory he also wrote The Puzzle Palace and Body of Secrets. I'm not sure how much material is shared between the three books, or if they're meant to be read in any certain order, but I'm plowing through The Puzzle Palace now.
OK, good, glad to hear that. I had sort of assumed that that was the case, but wasn't sure. It's a lot of material to slog through, but I find this stuff fascinating for some reason.
Specifically relating to the recent revelations, this book was where I learned of the NSA's "vacuum cleaner" approach, in which all available messages are collected -- in this case, it was trans-Atlantic radio transmissions being monitored by ECHELON. So, an American citizen in the UK calling an American citizen in the US would have their call collected.
The approach (collect everything you can at the trunk line or server farm) is very similar to the e-mail collection strategy that's being documented now.
In any case, it's wildly interesting stuff.