I got myself a short email at @ ymail.com and maybe I am going to use it soon. For the existing users is not such a big thing but for the new people that are trying to register with Yahoo it's an improvement.
It's better for typing but in general, I don't think typing is used very often when sending emails. In fact, there are also reasons for longer names to be better for some purposes.
hmm... I don't like their new addition at all... I guess the target is at the new peeps... however, yahoo! is starting to look more and more like google... when did yahoo! stop having their own ideas? I think google is on its way to eating everyone... even Microsoft eventually if they get asked to the table. "Hey, Microsoft... I made you a nice code cake..." Bammmmmmm!!!!!!!! *Powwwwwwwww!!!!!!!!!!!!!!!!!!!!! Where'd everyone go?! Hahahahahahahahaha *evil google laugh ^_^
in the registeration page where you put your choice of usernames, just to the right you click on the drop down box and slect ymail. Did that help?