I have been a user of Yahoo! since 2001. Back in the day, I used to love this service, and I don't remember the ads being intrusive at all. I wasn't a huge fan of the interface, but it was functional, so I didn't really care to switch to Gmail.
Soon flash ads started appearing. Every time I sent an email, I would look at an ad in the sent confirmation page. Then Yahoo! "upgraded" their service to the New Yahoo! Mail. This was cluncky as hell, and now the ads are far more intrusive.
Once I switched from IE to other browsers a few years ago, I didn't have to deal with ads, and this again made me not want to switch to Gmail because I didn't want to deal with the hassle.
The other day, I happened to log in to my yahoo email account without the adblocker extension, and I was reminded of how intrusive the ads were, and I might even say, they are NSFW in some cases!
I can't imagine anyone looking at this, and not getting annoyed. Makes me wonder, who makes these design decisions. At this point, Yahoo! doesn't have to innovate. They could just improve by imitating their competitors. The new Outlook service is an excellent example of a minimalism. Yahoo! could learn a lot from it.
I would love to hear from someone who is actually paying for a Yahoo! email account. What makes them pay for something that other services provide for free? I almost want to pay the premium, download all my email into Outlook, take a backup, and just never ever use Yahoo! again.