Yep. I'm having the same issue - with the "original" old version - the one that's current - AND - the new "beta"... All Yahoo mail is down, it appears, all over the country. Saw one post that said someone in FLA could access, and someone in NYC and in NJ could not... I'm in WA, and have been trying to get on since 8 PST. It's now 11:13 PST.
Check www.downrightnow.com for the status of web applications. It'll help you know if it's just you or if the problem is widespread.
Most people who are replying to these seem to believe it's due to Yahoo updating their Email service, and that it will take 2 - 3 hours before it's up again - however, I've also seen someone post that this has been going on since last night - soooo... Who knows.
It may even be that some servers got knocked out due to the bad storks - since someone in FLA can access, but someone in NJ, NY, and myself in WA cant.
Just be patient - this isn't the first time this has happened, and it won't be the last - but it doesn't happen often.