One of the major complaints about Yahoo!'s contextual ad program, the Yahoo! Publisher Network, was that the ads did not load as quickly as Google's contextual ad program, Google AdSense. Yahoo! has announced that they have made performance and style changes to the ads.
The changes you’re likely to see include the removal of ellipses (…) and truncated words, the inclusion of 40-character titles on certain ad units, and a change in the number of ads displayed on certain ad layouts.
Here is a screen capture of the before and after of the small banner ads, I have on some of the pages on this site.
Notice how they cleaned it up a bit and also dropped out the description part of the ad, for this specific ad block size.
Forum discussion at WebmasterWorld & DigitalPoint Forums.
Update: Search Engine Journal has a list of the changes made for each ad block.
* 234 x 60 and 468 x 60 ad unit size will no longer display a description
* Number of listings will change based on the following:
160 x 600 = 5 listings
180 x 150 = 1 listing
300 x 250 = 3 listings
336 x 280 = 4 listings
728 x 90 = 3 listings
