An SEOMoz post charts the positive impact having a Sitemap file can have on the speed of Google and Yahoo crawling and indexing your web pages.
The report seems pretty impressive and I myself feel that Sitemaps are important to have, for more sites. In fact, I recently added a Sitemap for this site, although, I really don't think it will help much with indexing this site any faster due to us being in Google News.
That being said, the Sphinn thread around this post has some quality discussion. I want to isolate one post from "IncrediBILL" who asks the question, is the Sitemap to credit for these sites getting indexed faster or is it FeedBurner?
Google acquired FeedBurner and FeedBurner is incredibly fast at picking up new content, specifically from WordPress blogs, which is what the study was done on. That being said, the report would have not shown an increase in speed to crawl if Sitemaps did not have anything to do with it. FeedBurner was a factor before the Sitemaps files were in place and they were a factor after the Sitemaps files were in place. So the only thing that really changed with this site (outside of Google changing variables, which they do often) is the Sitemaps addition.
So who would you credit for the faster indexing? Google's Sitemap protocol or FeedBurner? I'll poll it up:
Try not to use the "other" response. Yes, I know, I know.
Forum discussion at Sphinn.