I used to be on Reddit all the time. I had 9000+ comment karma, 1500+ link karma, and I didn't miss many front page posts. Reddit was a productive distraction for me at first. When I was in High School Reddit introduced me to a ton of interesting news, science, and of course funny shit that made me happy. I bought my first Java book because there were so many programming jokes in the comments that I wanted to know what it was all about.
After a while, I noticed Reddit was less and less productive for me. I had figured out which news sources the top quality submissions came from, and I followed them directly. I didn't need Reddit to teach me about the things I really wanted to learn about, I could find them myself. One day I said "fuck this" and quit cold turkey. Went from spending 1-2h a day on Reddit (or linked sites) to never going on it again. That was about 2 years ago, still haven't been back.
Then I got a software engineering internship and I was introduced to Hacker News. I had the same feeling I had when I started on Reddit. I was learning a TON and it was definitely making me a better programmer. I was being introduced to dozens of new technologies, frameworks, startups, etc. Now I'm starting to get that feeling that it's not so productive anymore. Partially because I know a lot more, and partially because an increasing percentage of the content is now opinion rather than reference. I still come on the site because it's a great way to keep tabs on the tech industry, but I can see an exit in the distance.
So there, that's my way-too-long answer to your question.