I am a co-founder of PhysicsOverflow (www.physicsoverflow.org), where I am mostly active these days.

For me personally, this site has unfortunately lost its usefulness for advancing and deepening my own physics knowledge, as most (even very advanced up to research-level) deep and interesting technical theoretical physics questions that contain LaTex are said to be not "conceptual" enough and are treated and closed as homework or too mathematical these days.