I just finished this last night and thoroughly enjoyed it. The concept that drives the story is very cheeky and fits perfectly with the evidence any of us can gather from our daily interactions online and in the real world. It's not short on "dad" humour that takes the edge off what could otherwise be quite confronting at times.
In many ways it feels quite similar to Flash Forward, which is high praise as I enjoyed that book just as much as this one, although Quantum Night has big philosophical and psychological aspects that set it apart. The story is intricate enough, with our protagonist's past gradually revealed to us through flashbacks and insights from his treatments, but it never becomes bogged down or confusing.
I find Robert J. Sawyer's style makes for very easy and enjoyable reading so I ate this one up in less than a fortnight. The characters are mostly likeable (most of the time) and the one really bad guy is only briefly involved in the story. That said, all the good guys do questionable things but that is part of what makes it so engaging. If there was one aspect that bugged me a little, it was that the background of general unrest -widespread rioting, etc. - seemed a little forced. But that was a minor gripe that didn't spoil anything.