If you want to know the number of pages, that Googlebot has crawled in your site for the last 90 days, then Google Webmaster Tools will helps you to find out. According to Googleblog, "We've been conducting a limited test of a new feature that enables you to provide us information about how we crawl your site. Today, we're making this tool available to everyone. You can access this tool from the Diagnostic tab. If you'd like Googlebot to slow down the crawl of your site, simply choose the Slower option."