I found my comments getting more guarded as people have poked holes in my comments for a long time, and I find myself writing more carefully. Also I've learned various phrases and terms I never would have learned elsewhere in other communities. In other words, my writing has gotten better, and as we know, writing is one of the best forms of thinking.
In terms of my career, sure, I've found many a useful resource on HN over the years, although, many of the URLs I've collected are left to rot in my bookmarking service, and I need to revisit them. But every now and then a game-changing tool comes out that revolutionizes my workflow, and for that I am thankful for HN.