Yahoo has changed their mailservice recently as a beta service. During the beta period, it was still possible to switch back to the old interface. As of today, that is no longer possible. Yahoo has removed the beta label, and it's mailservice is now the same for everyone. As you'd expect, Yahoo has added some features that will attract a crowd : sms service is integrated, and supposedly the service is free. IM is also integrated.

In short, the mail service has improved greatly in terms of performance and ease of use by putting ajax at work. Yahoo has done a good job in my opinion. I have to say though that, ever since Google started offering gmail, I have become addicted to gmail, mostly because of the way it handles and organizes your mail. No more folders and such and of course you benefit greatly from the supreme search algorithm Google is so famous for.

In other words, yahoo's mailservice is okay, better than most (hotmail, huuuu), but I prefer Gmail.