No, this is not another free directory for people to submit their blogs. Its the official blog directory from Google where all the blogs that Google runs to update news about their products etc. are listed, and there is no way you can submit your blogs or suggest anything to it.

Google blog directory is a listing of all the blogs which google runs. Here is what Google says about it -

Whether it’s a product or feature launch or a cool new initiative, chances are that you’ll read about most news from Google on one of our blogs. We started blogging in May of 2004 and now have a network of company blogs that cover topics as diverse as our renewable energy policies, product updates, developer challenges and code snippets, and information for advertisers and partners.

I counted the whole list and it was a total of 98 blogs, most of which run on blogspot.com and a very are subdomains of the main product like the youtube blog, orkut blog etc.
The categories and number of blogs are -

• Regional – 26 blogs of different regions for Google and Youtube
• Google wide – 10 blogs related to Google’s updates, policies blog, mac blog, OS and student blog etc.
• Products – 29 blogs updating with new releases or tweaks within the products of Google.
• Ads related – 14 blogs related to the ad services like adsense, adwords etc.
• Developer blogs – 19 blogs – For all the API related blogs etc.

You can view the latest post of any blog from the directory or subscribe to any blog. I had known of around 20-25 blogs of theirs, but 98 is a big number of blogs being managed by them and updated regularly with news and developments about the products.

You can check the Google blog directory here.