Many people tend to rely on Support guides, tutorials or articles from sites like Mashable and Search Engineland to inform them of new advances to platforms like AdWords, LinkedIn, Twitter and the like. However, a rich source of information can be found on the corporate blogs of companies like these. Product announcements, feature changes, tutorials, case studies and much more can be found on these sites. Here are a selection of those sites.
Here are some links to Digital and Social Media Marketing Blogs
Google AdWords Blog
Google Analytics Blog
Google Webmaster Tools Blog
Google Blog (including Google+)