I'm a huge Vinge fan, but I was really underwhelmed by Rainbow's End. (Was it aimed at the YA market and I didn't notice?) Hope CotS is better.
_Rainbows End_ is less fun than his other novels, but it deals directly with near-future issues in a way that only a few other SF authors are doing well (Stross, Stephenson, recent Gibson, and who else?). It changed how I think---much more than did, eg, _A Deepness in the Sky_. In terms of relevance to the times, I'd rank it next to _True Names_.
Of course, that mean it was probably only in the top 10 SciFi books of the year instead of indisputably the book of the year.