A fantastic book. It will really make you ache for more information, though. Why do ascended beings only hang around for a few years and where do they go? What fraction of living beings survived the Blight and the Countermeasure? What is the present-day status of Earth?
... a few years in realtime ...
In the Transcend, they can "clock up" to a very high level. Living a million seconds to each one that passes in realtime.
What would it take to create / adapt an intelligence that would last that long without falling into a very deep rut, as far as thinking goes? Maybe they've died of boredom, maybe they've discovered everything they originally sought to learn, maybe they've Sublimed (yes, I know, that's a Culture series thing) or otherwise gone to a higher plane of existence.
It would have been interesting to explore this further, but perhaps Vinge didn't think he could pull that off.