Years ago, when Google started offering over 2 gigs of storage on their mail solution, the world changed. I used to host my own mail as regular mail providers would give you a louzy 25 mb for a mail account. Not long after Google's mail introduction, which grows, the competition came out with big mailboxes too. Yahoo, and recently even Microsoft started offering more that one gig mail storage.
Yahoo obviously wants to shake the world - they just announced unlimited storage for mail. That is great of course. Although I can't imagine they don't make use of a FUP (Fair Use Policy) where storage is, in fact, not unlimited. Besides that, I think offering unlimited mail storage is over the top - they would have been fine by offering 5 gigs or so. Why go unlimited ? Who is going to use it all ??