Yahoo started with relatively modest offering of Internet directory - web links collected and posted on its website, pointing to Internet resources that two co-founders found interesting or useful for themselves.
It looks like the company hasn't gone too far from that original offering. I only know their mail and search services and both are copycats. Search hasn't become more competitive with bringing Mayer from Google, after she was demoted at Google.
It's pity that the company has gone nowhere after being the industry's darling and burning a lot of money that could bring much better results. They had some great engineers in their disposal such as Doug Cutting - one of creators of Big Data platform Hadoop.
From reading the book I can conclude that the main reason for eventual failure was in weak leadership throughout Yahoo's entire history. It looks like newer technology (and not only technology) companies thrive and attain sustainable future if their founders play stronger role, like in the cases of Amazon and Google.