Depends where you're going. Top companies like Google, Facebook, Microsoft, etc are looking for people who can pass some tough CS questions, whereas more standard corporate or mid-stage startups are going to be a bit more lax. I've seen everything from "parse this integer from a string without your language's built in parse function" to "build a small database schema using ER diagrams" to "write us a P2P chat server with a central login server".