From a technical standpoint, there's virtually no difference between these kinds of posts; they're all permalinked h-entries which house another, usually external, URL and which often contain no other content beyond that link. They differ solely in the microformat which annotates the link, indicating the intent of the post.
And intent make all the difference here. A like is supposed to convey that the author actually enjoys or appreciates the content to which the post is linking. A repost is supposed to convey that the author wishes, for some reason, to share that content on their own feed. A bookmark is supposed to convey that the author...ugh...err...
Wait...what is a bookmark supposed to convey, exactly? Other than that the author...you know...bookmarked a link?
It's clear that the semantics of a bookmark are a bit "mushier" than those of a like or repost. Likes and reposts, to some extent, reveal the author's disposition to the link; bookmarks don't really reveal anything other than that the author thought the URL was in some way "interesting" enough (for some definition of "interesting") to refer back to later.
According to the wiki page, common uses of bookmarks include
- building a "read later" list
- building up a digital library of online content
- sharing interesting content with others
Depending on what you want to get out of your bookmarks, your relationship to them will be different. If the sharing aspect is important to you, then posting them to your site is a core feature, and syndicating them to Twitter or Reddit makes a lot of sense. If, on the other hand, you're like me and you're just using them to mark articles so that you can read them later, then sharing them publicly might be less important, and you may not want to syndicate them at all. In that case, the bookmarks themselves might be a lot more ephemeral than other kinds of posts, if you choose delete them after you read them.
This all suggests, in my opinion, that bookmarks are fundamentally different from likes and reposts. It's much more plausible, I would argue, for someone to want a feed of bookmarks then it is for someone to want a feed of likes - even if, in my case, that someone is myself (hence my separate link feed). As I alluded to before, it's entirely possible to want to syndicate your likes, but not your bookmarks. I find myself much more likely to add a tag to a bookmark post then to a like post.
I suspect what this means for me is that I may end up developing some personalized and specialized tooling specifically around my bookmarks - maybe an easy way to manage them on the command line, for example. Time will tell.