Rather than speculate blindly, I wrote a simple mapreduce to check the web and find out for sure. The mapreduce scanned approximately 177 million recently crawled HTML documents, parsing and counting rel values in link and anchor tags along the way. In those 177M documents, I found just over 19 billion <a> and <link> tags in total. And of those 19B tags, 1.8 billion of them contained a non-empty rel attribute. […] This survey indicates that rel values are both widely and meaningfully used, with adoption being driven by a wide array of needs, such as semantic markup, search engine hints, client-side rendering, discovery and identity protocols, blogging, and/or content that can be later edited.