Well I don't know how many user across the globe felt a yahoo login service failure. It was quite evident around 11:00 AM London time when I was unable to login into few of my yahoo accounts. Be sure I was not using invalid username and password. Just within couple of minutes the service was restored. I think
yahoo might update on why this has happened. No update as of now.
Update ( 30-Jan-2008 ) : There has been an another such outrage from yahoo. The user are unable to login into any services from yahoo including popular chat,mail and flickr accounts. This time it has lasted more than 5 minutes. It started around 04:45 AM London time. There is also a small change in the user interface of login screen. The sign-in seal show "Are you protected ?".
Update (30-Jan-2008) : Its almost more than half an hour and yahoo login services are still down. I am not sure about premium ( paid ) services. I have tried almost 20 times but I am unable to login. If I am not wrong yahoo usually block the account after few unsuccessful attempts. But there is no such warning. I tried to recover my password by providing my credit card information but it gave a
programming exception ( FEATURE_ERROR_USER_OPEN_NO_ACCESS ). Well hold one if you thought it is happening with all yahoo id's then surprisingly its not. I have tested it on few other id's, a couple of them were found to be working fine and there was no exception error even if I tried to recover password ( though I don't have to as I was able to login ).