HN is lightweight in some ways, but also quite bad in others. For example, every single time you vote on anything, the site sends back a 302 redirect and then a copy of the entire page's HTML in response. This means that every vote results in a response that's usually around 10KB gzipped. As of right now, for me, voting on any comment in this thread currently causes a 14KB response and takes about 1.3 seconds to fini…
Also, worth mentioning the insufficient formatting features. Quoting is not supported, and is quite important for forum discussions' UX.
Exactly