<<We are thrilled to announce the open availability of the Yahoo! Mail Web Service, web service for Yahoo! Mail (accessible via SOAP or JSON-RPC). With the Yahoo! Mail Web Service, you can connect to the core mail platform to perform typical mailbox tasks for premium users such as list messages and folders, and compose and send messages (you can also build mail preview tools for free users with limited Web Service functionality). >>

http://developer.yahoo.net/blog/archives/2007/03/mail.html

Hmmm... useful if your into that sort of thing i suppose...

yeah I kinda dropped the info nugget here ..
http://blogoscoped.com/forum/90226.html#id90332

...and I do think its now going to be a big challenge for Gmail to keep up!!