1. whether or not the page has already been submitted to HN
2. how many comments, if any, have been made in HN discussion about the page
My preference would be for a way to add that information to the page dynamically when the page is first loaded, on the server side, so that no client-side scripting (i.e. JavaScript) is necessary. If for some reason it is decided that it must be done with JavaScript, though -- well, I guess beggars can't be choosers, as they say.
As far as I'm aware, no reasonable way of doing this exists right now (short of something complex like automatically searching HN and screen-scraping). I'd really appreciate an API for this kind of thing being added to HN (and reasonably well-documented) so that I can make use of it on a site written in Ruby (not Rails, mind you).