They use Facebook and Twitter so you can participate in the big group there, but you can also or alternatively post here to discuss Dune with other happy mutants.
I guess it depends on whether everyone has read it or not if we get all spoilery.
I’m listening on the audiobook at audiobook.com - I signed up for the free trial using the code hop2 so I get two free books. It appears that it won’t start charging me until I trigger it to, which seems decent of them.
Like I said, it’s been a while since I read Dune, so limiting to chapters is going to have me digging it out of the bookcase, dusting it off, etc. Also, I will admit to having stopped after Children of Dune because every person I’ve ever spoken with who read anything further said it’s pretty much crap.