"Google Related is a browsing assistant that offers interesting and useful content while you are browsing the web. For instance, if you're browsing a page about a restaurant in San Francisco, Google Related will assist you by displaying useful information about this restaurant such as the location of the restaurant on a map, user reviews, related restaurants in the area, and other webpages related to San Francisco restaurants - all in one place," explains Google.
If you go to the Wikipedia article about Adele, Google Related shows 5 YouTube videos, 5 articles from Google News and 5 pages from Google Search.
Google Related is another feature that requires sending the list of all the pages you visit to Google's servers. To find related pages, Google needs to know the URL of the page you're visiting. The so-called "enhanced features" (PageRank, SideWiki, Google Related) send Google a lot of useful data. One of the most interesting ways to use the data is a feature that shows if a site is slow. Like all the other Google Toolbar "enhanced features", Google Related can be disabled from the "Options" dialog by clicking the "Privacy" tab.
Apparently, Google Related only works if you've configured the toolbar's search site to be Google.com (United States of America - .com), so you may need to change this setting to enable Google Related.