FWIW "Billions of dollars" should be considered in the context that 1 million people * $1,000 = $1 billion. The US is ~300m people. So, this headline is something like "1/3 of 1% of the US is putting an extra $1,000 in their 401k recently" (really more like 1-2% of the _workforce_ but the point remains)
I use this service and I like it. Many blog posts and engineering discussions tend to treat tools in isolation -- you're learning about Redis or Rails or Ember only. Being able to meet other engineers who use the same _combination_ of tools can help you learn about higher level design patterns and the interactions between the tools.