Generally I only bookmark stuff that's going to be useful to me at a later date.
What I'd really like is for the bookmark to also cache the page locally so that even if I click the bookmark at a later date and the site has gone I can still read what was on the page.
I'm a paying user of yours so I don't have any specific problem with you or historious, but I don't like that you're offering a free month here. I'm sure it won't really have any impact, but in theory by rewarding people who say "have you tried <product>" in a HN comment you're incentivising people to make those comments, essentially offering people the chance to use a referrals scheme without it going through referral links.
That's true generally, although it doesn't really apply in this case. I don't usually give free months to people who mention historious, I was just happy to see a mention and gave a freebie.
Arguably, the free bookmarks you get through referrals are more useful, since they don't expire...
http://www.zotero.org/ can do this. It can make a snapshot of the page, and also a copy of all attachments on it (especially useful for pdfs, images etc.)
What I'd really like is for the bookmark to also cache the page locally so that even if I click the bookmark at a later date and the site has gone I can still read what was on the page.