Bing Webmaster Site activity combines data from Yahoo! and Bing for these stats. It shows the number of clicks from different search engines, number of times a site’s appearance on search engine, crawled pages, crawl errors, total indexed pages. It’s nice to align the number of pages crawled and the crawl errors, but as with most graphs like this, it’s the trend that matter the most here. If all of a sudden the graph flat lines at zero (except at the crawl errors), there must be something wrong.