Search Engines crawling / indexing non HTML-content
An interview published on Guardian with Dan Crow, the director of crawl systems at Google.
Why is understanding of how Google crawl your web site important?
If you understand what content that is "crawlable" and not, on your website, you stand a better chance of achiving visability on the web for your products and services.
On the same topic comes a blog written by Jill Wahlen, summarizing a Dan Crow presentation on how to get Your site into the Google system - increased visability in the organic (non-paid) search result.