Thanks, this helped me a bit. Ah!...I forgot to say something..
I am actually developing a web application. And, after some thinking, I have understood some specific points.
Some would like to use yahoo! because of what it
has to offer , while some would use it because the
way it has to offer -> functionality and user interface
while others might use the email client ...
Any more suggestions/replies/comments welcomed. A complete thought process....