what is sandstorm?
Additionally, as long as the question "WTF IS THIS??" is not forbidden in the HN comments, even those lacking the domain knowledge, or a sufficiently useful description on the site itself or a useful Wikipedia page, I think the extent to assume is fairly low.
That is, I think it's safe to assume the internet, and its users, exist, and that the reader is sufficiently intelligent to make use of the resources available to them, when writing a post to publish online, if it's not intentionally an introductory post
It makes sense for some services that are fundamentally user-fragmented (File backup/Evernote/Flickr) but less sense for things that require multiple users to be credentialed like social networking, since social networking structurally benefits from everyone being on the same service.