I think a lot of great discussions are being had in private Google Docs. I also think that a lot of this discussion gets completely lost and/or forgotten.
"Quick Takes" can act as an alternative. Arguably, this is a good place to try out smaller ideas and/or get feedback on them. Any early discussion on quick takes is arguably more useful than similar discussion with Google Comments, as it would all be public.
Personally I've been enjoying my quick take use. I feel like I could get a good amount of discussion and interaction, for the level of work I'm required to put in for the post. I might later convert some of this into full regular posts, but I don't feel a rush. I also do a lot of writing quick similar post to my Facebook account, especially if they seem like a better fit for that audience.
Likewise, I feel more comfortable commenting on other people's short takes than I do private docs, because that way it feels like my comments are more likely to be useful. With Google Docs it's easy for a lot of work to get totally ignored and then lost.
Obviously, I realize there are some good reasons/circumstances for privacy and for Google Docs. But I suspect that these benefits are narrower than some assume. Being more public has some downsides, but I think it's often possible to overcome these downsides - after which the net-upsides both personally and collectively can be significant.
This comment has gotten me to think about this, and I have a corresponding public response there with my point.