Yahoo Site Explorer (http://siteexplorer.search.yahoo.com) is a service provided by Yahoo that shows what the Yahoo search engine knows about your site, specifically which pages are indexed, and the number of inbound links. If you register, you can submit a feed to Yahoo to ensure that Yahoo knows all your pages.
The most useful part of Yahoo Site Explorer is the number of inbound links. As we all know, the link: command provided by Google is notoriously inaccurate, and it appears to me that the count returned by Yahoo Site Explorer is more reliable. In addition, Yahoo has made it easy to exclude inbound links from the same domain or subdomain. This is helpful as webmasters often want to know both the total number of inbound links, as well as the inbound links from external sites. It’s true that the above information was already available on Yahoo before Site Explorer, but it is much easier to get at the information now.
One nice feature about Yahoo Site Explorer is that it’s easy to explore different URL’s. For example, as you are looking through all the pages that link to a particular site, a “Explore URL” button appears as you mouse over each page. You can click on that button and instantly get the information for that page. That was very convenient for me.
I also authenticated my site (you’ll need to use your Yahoo ID) to see what additional information I can get. I found out basically the only benefit of authenticating your site is that you can send a feed (basically a sitemap) to Yahoo, and Yahoo tells you when its crawler last accessed that feed. This is less than what I was hoping for. For example, Yahoo does not tell you it cannot find a page listed in the feed, nor does it tell you how many times your site was clicked on from within Yahoo Search.
Overall, Yahoo Site Explorer is a useful product for users to find out more information about a site/page. As a webmasters tool, it lags behind Google’s Webmasters Tool product. I would recommend that you authenticate your site through Yahoo Site Explorer so that you can submit your feed to ensure Yahoo picks up your new pages, but that’s pretty much it.