SEO (search engine optimisation) is debatably one of the most important things to get right in a website that needs web traffic. If your web traffic is driven by search engines, you want to give the search engines anything and everything they could need to connect someone's query with your site. Especially as traffic from search is effectively free traffic.
Google have webmaster tools available which give you access to stats about your site (assuming you have tracking on your site), crawling errors etc. They have associated help sections and even have an SEO guide available for download.
What Microsoft have released is an IIS add in that gives you a huge amount of stats, finds issues and provides diagnostic information about any site you point it at. We pointed it at the W3C (World Wide Web Consortium - Home of Web Standards), limited the tool to 5000 links and set it running.
It found more than 19,000 violations:
It ranks these by SEO, Content, Performance and Standards and gives an indication of the severity.
The thing you notice when you get going with the tool is the extent to which you can drill down and the immense utility of the information it exposes.
Did you know the content of the <title> tag shouldn't exceed 65 characters? search engines generally truncate the text after that.
Here's a hastily thrown together image of the other menu options:
It's currently in beta and only works in IIS 7 so that means it's limited to Windows Vista and Windows Server 2008. I think it'll quickly become a mainstay of the SEO optimiser's arsenal. Find out more here: Scott Guthries blog