Before the weather report was issued there was some recent chatter in a WebmasterWorld thread this morning on a Yahoo! Search update taking place.
I definitely see some major changes. The rankings seem to go back to the old results from late 2006. Which is good for the categories I watch. The update in January definitely had some spammy sites getting rewarded. So this new update is fine with me.
We are re-indexing content on the web to launch this change, and you should immediately begin to see the changes on Yahoo! US, Yahoo! Japan and Yahoo! Korea. (Other regions will roll-out in the future.) This will be accompanied by the usual ranking changes and page shuffling that is typical of weather updates.
This is probably why it took so long for NOYDIR tag to be released, it seems to have required a global update to all of Yahoo! Search properties.
Forum discussion at WebmasterWorld.