Most of the books I've been reading on the Kobo app aren't purchased from Kobo so they don't have the Pulse feature. The one book I did read that had Pulse had no other comments but mine!
I think it might still be early days for the Pulse feature. I would encourage people to use it because I absolutely LOVE the idea, but I'd imagine that unless the book is REALLY popular, we probably won't be seeing much action on it for a while.