I've posted a lot recently about developments to Google Webmaster Tools so thought I'd summarise all the ways Google Webmaster Tools is now helping webmasters manage their sites and the SEO benefits from these developments

Accurate information on 404 errors. Google now provide the source of the 404 error, so you can track back the error on your site and correct it. Broken links impact on search engine listings as when they crawl websites, 404 pages make the site look like a site with no integrity.

You can review the content on your site for duplicate meta descriptions and title tags, which can make the site look like it has duplicate content on it. Once again these duplications are shown with the pages that are affected, enabling you to easily resolve issues with the site.

Google are rolling out a new tool that enables them to warn webmasters when there is a possible security risk on their website. Hacking can seriously impact the rankings of your website within the search engines, so being aware of a potential risk before it happens is a useful benefit.

Matt Posted last year about using Google Webmaster Tools to tell Google what country your customers are in.  This is a great way to start with Geo-locating your website

Added to these items of goodness from Google is the ability to see the most commonly clicked searches for the site - a great way to find long-tail keywords for blog topics.

You can also submit sitemap's to Google and review the content of your robots file, helpful for directing the search engines to the right places on your site.

All in all, reviewing your site in Google Webmaster Tools, is a great free way to ensure that the SEO work you are doing on your site is working