Helsinki-based AddSearch's thesis is that the standard Google-powered search for websites basically sucks. As they start adding more and more features to their product, you can see that no one really has looked at what features or material should be included in in-site search.
Case in point- they've just added Twitter search to the same drop-down search bar embedded on websites. So if you're looking for topic covered by a media company, for example, like something that was once breaking news, you'll be able to find those tweets alongside full news articles.
In all editorial disclosure, we should mention we're one of the first users of AddSearch, which means you can test it out using the search bar in the top right and see article results as well as Twitter posts by ArcticStartup that are relevant to your search.
If anything, AddSearch is probably worth the pricing just because it makes the search bar an actually interesting part of your website - for both our side and the readers side. For website owners, you can tweak certain searches to make sure the right About Us page is right at the top when someone searches a writers name, for instance, and you can see all sorts of fun facts about what people are searching for. We haven't played with it as much as we should, but checking search results lets us know what our readers are finding interesting.
And for readers, it's convenient to stay in the same webpage when searching for a new page to go to, in case you need to reference the page. Additionally it's nice to see a screenshot of what the page looks like, so you can better find an article you've already read based on the header image, for instance.
The company says that Facebook support is underway. Additionally the company pitched this past weekend at SXSW, so they should be getting some good buzz from that exposure.