Earlier quoted context omitted.
I think the most obvious example I would add to this list you are thinking of would be livejournal. I also had a handful of SoundCloud-like medium scale music sites that I went to, like Purevolume. I also remember this as a time when Google didn't yet have a reputation for abandoning everything they touched, so you could get inspired by, say, Google Knol or Google Wave. I had hope that Google Reader might grow into s…
There are no real barriers to blogging or using an RSS reader if you want to. (RSS feeds are less ubiquitous than they used to be but they're still common.) And, of course, for saving and sharing bookmarks, it's Pinboard that's buying del.icio.us. I never really tried out Wave but Knol suffered from the problem you'd expect if everyone gets to write their own self-promotional competing article on a topic.
I'm perfectly aware of this and have used RSS feeds on a daily basis for more than a decade, so I'm not sure what's being suggested here.