I have been using Tumblr links for the website's SEO, it was very good to deliver results. Long ago I left using it. Now I have a question, is it worth to be used for backlinking?
Yes, Tumblr blogs are SEO friendly. Tumblr has its own search engine that helps users find the content they're looking for, and Tumblr blogs often show up in Google search results as well. In addition, Tumblr allows users to tag their posts with keywords, which makes it easier for search engines to find and index them.
It all depends on the industry, you can get a few. You always need to focus on getting links from which there is a chance to get traffic.
Tumblr is my favorite Web2.0 as when you're listed for your tags, you get links to your tumblr from the main site.