Nobody should be scared that what they have to say might be short or brief, not everyone wants to do a long post. Some people do, some people don't, but I read them all, because I might miss something interesting.
I have a sneaky tip for the CbC discussions though. Get some of those little reusable coloured tabs/page marker thingys. And then as you read through, just use them to note anything interesting. They won't harm your books and you can re-use them. Soon enough, you'll have a load of good quotes and starting points.
Some chapters are more difficult than others though, and I think starting a new books is slightly odd, as we've got used to Book 3. It'll pick up I'm sure.