You may have noticed increase in delays and rejections from Yahoo. I am certainly seeing a lot of customers complaining and hearing a lot of other delivery people commenting on problems getting mail into Yahoo. I have even heard from multiple ISPs that are struggling with full queues and delayed email.
No solutions or suggestions right now, just that everyone is having problems right now. I expect it will take some time for the backlogs to dissipate, even after the underlying problem is fixed. If I hear anything more I will post it here.