Yahoo mail turned 16, and now it is having a new look and new features like themes etc.
The most noticeable changes on yahoo mail is the storage space and the themes. Now yahoo offers 1TB of storage space for each user.
Now you can change the theme of your inbox, there are many Flickr image based themes are available which you can choose.
Easily search for all the mails from a specific person
Now Yahoo also offers disposable email addresses, mail forwarding and POP access which where accessible for the Yahoo Mail Plus users only.
You can enable/disable conversations (grouped messages) under Mail Options => Viewing email.
You can read more about disposable email addresses here, you can create disposable email addresses and also enable SSL under Mail Options=> Security
You can also create an extra email address which will work same as your existing email address