Dear Yahoo! Mail User,As noted before, this is in direct response to Gmail, showing that the power of capitalism extends even to free services (if you call seeing ads while you read your email "free").
Thanks for using Yahoo! Mail. It's our goal to offer you an email experience that makes it easy and enjoyable to stay in touch. Periodically, we make service changes to enhance that experience for our users. As of June 15, 2004, you'll enjoy the following benefits:
Increased storage capacity – from your current level to 100MB (still a big difference from the free 1G on Google, but a big improvement)
Increase in total message size to 10MB (I think the old one was 2MB)
A streamlined interface that's even easier to use
Update: I should note again that this is for the free level of service only. As Techdirt points out, there is even more storage - 2 Gigs! - for the paid level.