I like the new interface. However it would be great can add your own images to the background or add more personalization options.

And please, read your audience: Delete all the messages in old accounts (or accounts connected to another main inbox, very usual in work accounts) or add pop ups that can't be unabled in the main page are horrible ideas. I know that Yahoo is in a difficult period, but it was a great service and it could be in the top again, maybe in another area. But for achieve this it's very important listen the audience opinion. I can't believe that a service famous for "Yahoo Answers", where a huge community was listened, now can have this kind of problem.

Good luck