Excellent post on the basics! As you mentioned in your post, the real work begins once you have the algorithm in place.

Scraping is a challenge as Readability, boiler pipe and so on are only so effective.

Sentence parsing is extremely tricky. Support for surnames, urls, ellipsis, quotations, and all the other weird language things.

This is the simplest implementation of textrank I've seen, and a lot of credit to the author for writing it in such a way. If anyone is interested, you can find out more about textrank from this academic paper which explains it quite nicely (http://acl.ldc.upenn.edu/acl2004/emnlp/pdf/Mihalcea.pdf).

Note: just released http://summary.io