The Yahoo Search Blog announced yesterday a new crawler behavior for the newly trained Slurp (Yahoo's search crawler). So instead of Slurp running around your site like an untamed animal, it is not more proper and polite.
I looked through the forums yesterday morning to find people discussing any ranking or traffic changes seen at Yahoo but came up with nothing.
Now, however, people are buzzing a bit about traffic changes seen from the Yahoo Search referrer.
One person saw a drop in traffic:
I just ran through some of my results page ranking for Yahoo and man-o-man have I taken a nosedive. Looking through G-Analytics its as if my site ceased to exist on Yahoo on August 18th.
An other person saw a huge spike in traffic:
I don't know if it's significant... but my Yahoo traffic quadrupled today and now outstrips my Google traffic. I don't know if it's a blip but it appears to be an improvement in traffic from Yahoo across the board and not from a few specific keywords.
Typically the forum threads come before any official Yahoo "weather report," but in this case, they came in after.
Forum discussion at Search Engine Watch Forums and WebmasterWorld.