We are almost finished building a tool (Thoughtly) that quantifies people's written contributions online, so people can display their life experience in a broader context. We want to make sure our first version accounts for platforms and data sources that users find the most valuable. Do you publish academic papers to sites like Mendeley? Are you an active Redditor? Stackoverflow? What are your go to sites to engage in intellectual dialogue, besides HN (and social platforms like Twitter/FB)? With so many data sources and API's to choose from, we want to make sure we account for what people care most about! Thanks. http://thoughtly.co
I contribute a bit to Quora. Despite the bad rap that Quora has on HN, Quora does a really good job of curating posts, and there are a lot of extremely high quality posts related to software and startups. It's a lot less nitpicky than HN because anecdotes and opinions are perfectly fine on Quora.
I do a lot of very informal writing online, mostly in Subreddits related to my field, but also in comments on news articles at places like Wired and Ars. I find that you learn almost as much from the (non-insane) comments as you do from the articles themselves. This is probably the same reason I use/read Reddit.
I do have some more academic writing published on Academia.edu and SSRN, but I don't engage in discussion there.
Best of luck!