Yahoo recommends that webmasters sign up with Bing Webmaster Tools and use that as Yahoo shuts off Site Explorer.
Yahoo makes it sound like that you won’t miss the old Site Explorer but I find it hard to believe that Microsoft will provide detailed link data for competitors. Of course there are plenty of third party tools to get at this data, such as Majestic SEO and SEOmoz but with the loss of Site Explorer, there will likely be no search engine-provided look at your back links.
source: Search Engine Land
I’m a fan of Yahoo Site Explorer and will miss it as a link intelligence tool. Back in 2006, I released a search plugin for Yahoo Site Explorer. With its demise just around the corner, I put together an OpenSearch plugin for Open Site Explorer (SEOmoz). You can install it from the Mycroft website or right here. Enjoy!