It can do something as simple as a site: search on Google, but you can string configs together to join up 20-30 sites together, create tabs to split out by sentiment, split out by number or dollar ranges, etc. etc. I have barely scratched the surface with the Blades there now, hoping to see some creative ones surface.
Well, yes, if you don't mind typing or pasting the same combo of 20-30 different search operators in Google.com, it can be done there.
But there are some other subtle differences: you get thumbnail images with search results (if available) with Blades, and you don't get a captcha to prove you're human if your search volume or rate is out of bounds on a Blade. (These are features of CSEs, not something I've hacked.)
Also, FWIW, the HackerNews blade doesn't return anything (I tried some pretty basic searches on it.)