I have a good dozen websites listed under my Google account in Webmaster Tools. In case you do not know what that is, it is a service for webmaster to verify domain ownership to get additional information about the status of each website which is especially important when it comes to that site's search visibility.
You can manage crawl rates, see errors, get suggestions and can look at the latest important issues that Google identified while crawling the site.
Those information were only available after clicking on a site in Google Webmaster Tools previously which was not a issue for webmasters with one or two domains listed there, but could very well have been a deal-breaker for webmasters with dozens or even hundreds of verified domains. Imagine having to click on each domain to check its health status. This would take quite a while and needed to be performed regularly to make sure nothing is ever missed.
Google yesterday made the announcement that they have redesigned the Webmaster Tools start page.
Instead of just displaying a list of domains there, the page is now showing site health for every domain right on the homepage.
Webmasters now see on first glance if something's wrong with one of their websites. Sites with health problems are listed at the top of the list. Warnings may include that malware has been detected on the site, that important pages have been removed or that the robots.txt file is blocking important pages.
Each site is displayed with a thumbnail screenshot and link to manage the site in Webmaster Tools. A click on a problem opens additional information about the problem detected on the site.
Susan Moskwa, Google Webmaster Trends Analyst, notes that Google is using the display currently only for accounts with less than 100 sites listed. Webmasters with more than 100 sites will see site health at the top of the Dashboard for each site. While I'm not 100% certain it seems to suggest that accounts with more than 100 domains still have to use the old way of verifying that everything's all right with their websites.
Google plans to expand the site health notifications in the future to include additional issues (currently only malware, removed urls, blocked urls are reported).
I personally like the new layout, as it speeds up the process of making sure that no potential issues are missed when using Webmaster Tools.