I believe there are two new features now in Google Webmaster Tools. They are the ability to test sitemaps before submitting them to Google and testing crawlers specifically for Googlebot-Mobile.
Testing Sitemaps
Don't you hate it when you submit a sitemap to Google and you have to wait to see if there are issues with the sitemap file? Google now lets you test your sitemap files before submitting them!
Here is how it works, you go to Sitemaps under the Site Configuration link in Google Webmaster Tools. At the top right there is a new button that reads "Add/Test Sitemaps". Click on it and you can plug in a URL and then click on the "test sitemap" option:

Then Google will run the test:

When the test is complete, you can view the results:

And then here are the results:

This is incredibly useful!
Googlebot Mobile Crawler Test
Google also added to the Crawler Access a way to test your site with Googlebot-Mobile. I am not a 100% sure if this is new (I am told this actually isn't that new but they did add Googlebot-Mobile for Smartphone), but I am told it is:

New Design With More Details
Now statistics from Web, Videos, Images and News are featured prominently. This lets you see how many items of each type were submitted (if any), and for some content types, we also show how many items have been indexed. Sitemap errors and warnings are now grouped.
Forum discussion at Google Webmaster Help.


Comments:
Rob Abdul
01/27/2012 12:18 pm
Yet another reason why Google Webmaster tools are far superior than what Bing has to offer.
Christian Oliveira
01/27/2012 12:40 pm
As you say, I think that the Googlebot-Mobile User-Agent was in that menu already. The one which is newer related to that is under Diagnostics->Fetch as Googlebot, where you can select the new 'Mobile-Smartphone' option in the dropdown Menu.
Sergey S, CUA
01/27/2012 04:39 pm
Because Google tracks visitors in order to display best matches, there's really almost impossible to find out what your site's true position is (SERP). How about a tool that will give you a SERP position, based on submitted term(s) and domain?
Door Handles
01/27/2012 05:34 pm
This is good to see. I like the idea of being able to test before somthing is made commercially live. The data will be so valuable too as a means to measure.
Megan
01/28/2012 05:30 am
This is better, as i was waiting for sitemap issues. However can google give a report showing page rank of backlinks?
Jovy
01/30/2012 09:39 am
Basically a remarkable feature in Google Webmaster Tools. Can be helpful to assure tha what you will submit no longer have any errors and so you will be assured that when you submit the sitemap, it will be properly compiled.
Christy
01/30/2012 10:56 am
Google also has a new way of displaying errors, which the company says better exposes what types of issues a sitemap contains.
pervezalam
01/31/2012 05:01 am
These two features will help to find the quality of sitemap and behaviour of google webmaster for the site map to test it and to identify the problem before submitting. Great Feature!!
ildolce
06/20/2012 01:56 pm
Why is it possible that google don't identify a mobile sitemap?