Yahoo has been forced to throw in the towel quite a few times over the years. From search to music to travel, getting out of markets may arguably be the one thing Yahoo still does well.

And the list of markets Yahoo gets out of continues to grow. Yahoo’s latest shuttering: its AdSense-like ad network, Yahoo Publisher Network (YPN).

Yesterday, YPN publishers received an email which reads in part:

Yahoo! continuously evaluates and prioritizes our products and services, in alignment with business goals and our continued commitment to deliver the best consumer and advertiser experiences. After conducting an extensive review of the Yahoo! Publisher Network beta program, we have decided to close the program effective April 30, 2010. We expect to deliver final publisher payments for the month ending April 30, 2010 to publishers no later than May 31, 2010. All publishers eligible for 1099s for the 2010 tax year will have those mailed by January 31, 2011.

Because our content will no longer be delivered to your ad unit spaces after April 30, 2010, we recommend removing all YPN ad code from your pages by that date.

Yahoo is encouraging YBN publishers to sign up with Chitika, which is already courting YPN publishers.

Yahoo’s move to close YPN isn’t entirely surprising. It launched five years ago but has never put a dent in Google’s AdSense dominance. Given where Yahoo is at as a company, ditching YPN is probably a sensible move. Yet at the same time, it’s another reminder of just how far Yahoo has fallen.

Paid search is a multi-billion dollar market, and a good chunk of Google’s revenue derives from its AdSense publisher network. While Yahoo may be trying to focus on other things, one has to ask the question: if Yahoo is going to cede victory in the most lucrative online markets, how exactly does it expect to revitalize itself?

Cost-cutting and business divestitures may have a positive short-term impact on the bottom line, but the top line matters an awful lot too. At some point, Yahoo is going to need to show that it can deliver top line growth. And that rarely happens when a company’s favorite pastime is throwing in the towel.

Photo credit: Hoggheff aka Hank Ashby aka Mr. Freshtags via Flickr.