Yahoo Sitemaps help you get crawled.
Yahoo sitemaps go back a ways, but most folks I talk to are all about the Google buzz. Yahoo uses a proprietary format for their sitemap as well but the structure is easier to create. Simply create a .txt file and copy each URL of your site on a new line. Use the entire URL beginning from the http:// and you have yourself a Yahoo sitemap! You will need to store this file somewhere on your server. A sitemap creation service can automatically do this for you making your life easier and eliminating the need for you to keep your sitemap up to date.
You can name the file anything you like, but Yahoo uses the example of urllist.txt on their website. You can use the Yahoo Submit page to submit your sitemap to their crawler. This is the same page that allows you to submit your homepage to their crawler. As with any good Engine, they always remember to tell you that they don’t accept all entries.
Any good sitemap for a good website ought to be collected and spidered by Yahoo, but if you don’t create the file properly your sitemap may be the one getting rejected by them. If you give this an honest effort it isn’t difficult to do. One page of your site per line using the full URL, save the file on your server, submit it, you’re done. In the future, you just update that file and they will continue to spider your Yahoo sitemap as they make their rounds.