I'm most of the way through A Deepness in the Sky; I'll have more to say about it eventually. But one thing that I keep finding interesting about it is that it makes clear (without ever explicitly saying this) that in a sufficiently technological society, control of communication systems (which is to say, control over the data that people receive) essentially becomes control over (perceived) reality.
You can see vague approximations of that idea in the real world, of course: control over the media begins to approximate control over perceptions. Just look at politicians' attack ads (the sort that they eventually have to apologize for because they contain mistakes and/or lies, but the apology is rarely as widely seen as the attack).
Of course, in real life we have a multiplicity of data sources. And Vinge makes clear that the computing resources required to actually go in and change a multiplicity of data sources are huge; it's possible that without something like Vinge's setup (in which, to describe it very loosely and sans spoilers, one group is vastly technologically superior to another), enough computing resources to spoof all available data sources are unlikely to exist.
Still, interesting food for thought. And I think the sound-bite version makes a nice little geek mantra of sorts: Control of communication is control of reality.