On-Topic: Anything that good hackers would find 
  interesting. That includes more than hacking and startups. 
  If you had to reduce it to a sentence, the answer might be: 
  anything that gratifies one's intellectual curiosity. 

  Off-Topic: Most stories about politics, or crime, or 
  sports, unless they're evidence of some interesting new 
  phenomenon. Videos of pratfalls or disasters, or cute 
  animal pictures. If they'd cover it on TV news, it's 
  probably off-topic.

I feel stupid, but just don't get it. Why should I unfriend them for liking some rock band?