Yahoo mail hasn't been down once for me today. I think the "outage" isn't as wide spread as you think. Have you checked your firewall?
We can still check two of our accounts (the most important ones).
I get an HTML page with the text:
Sorry, the page you requested was not found.
Please check the URL for proper spelling and capitalization. If you're having trouble locating a destination on Yahoo!, try visiting the Yahoo! home page or look through a list of Yahoo!'s online services. Also, you may find what you're looking for if you try searching below.
That doesn't seem like a firewall/networking problem on our end.