Any serious technology-enthusiast knows that Yahoo within the past three-four years has been producing awful products, similar to that of Microsoft. Below will conclude really where Yahoo has failed in former years and what it needs to fix asap (whether they become bought out by Microsoft or not)

Their Email System
Factors like Spam Protection, Real-Time email updates on the fly, and advertising will push any new-user to Gmail. You might say, well why Gmail has Ads too! Gmail has ads that are non-intrusive, and all flashy. They have basic text links not built into where you will most likely NOT be clicking to access a new email or update a contact.
Their Failing Ability To Innovate
Yahoo is acting too much like their soon-to-be-predecessor (Microsoft), as soon as Google had created Gmail with contacts built-in to the email platform, Yahoo was soon to jump onto the innovative-bandwagon. However, by that point all the individuals who had been using Yahoo for so long (myself included) switched to Gmail.
Yahoo’s ability to innovate in just one product alone (their original selling product) no longer works.
This is why companies like 37 Signals will prevail in the future and not companies like Yahoo because they understand the fundamental concept of post-dot-com boom websites: simplicity, ease-of-use, and innovation in favor of the user. One-stop-portal-like websites were a thing of the late-90s. Wake up Yahoo… or rather (Microsoft) .