people on HN probably not that much, not sure. Out in consumer-land it's used quite a bit depending on your target demographic (>83% of US women 25-54 for example). Lots of growth outside of the US as well. I sometimes work with designers (interior, architects and the like) and they seem to use it A LOT. Decent amount of traffic from Pinterest on some sites as well, especially on long-tail stuff. Advertising options weren't available in my country previously, so can't say anything about the ROI.