When I envision a "commonplace book" as you've laid it out, I envision certain websites that are maintained and curated by one person or a small group of people, about one subject or a small set of related subjects, like the following:

- cat-v.org - Looks like a brain-dump on the topic of unix and programming by a now-deceased programmer

- wimp.com - An archive of popular videos from around the web

- textfiles.com - A massive collection of text files, mainly from the BBS era but includes some from the internet too.

- Be kind, unwind - A collection of "chill" music

- Very specific tumblr pages that are careful to only post/reblog a certain topic of content

- Pretty much any blog that has a well-defined topic (as you've said)

If you get rid of the "about one subject or a small set of related subjects" constraint, it just seems to me like you're making a public notebook. If you get rid of the "maintained and curated by one person or a small group of people" constraint, it seems like it just becomes a hubski/tumblr/twitter tag or subreddit, or wikipedia[1][2]. I'm super interested in the commonplace book idea, and have been toying with the idea of making my own website to start dumping my brain about a few subjects and creating some awesome resources. Hubski seems like it isn't quite the medium for this sort of thing, though.

[1]: Some wikis are amazing for the "collection of information", too - Obviously there's wikipedia, but the Arch wiki is a fantastic resource for Linux-related information. Maybe there should be some sort of hubski wiki?

[2]: side note, I've stumbled across a few wikipedia users' userpages - some of those are pretty good commonplace books as well.