Most of interviews I've done to candidates ended up in discussing technology trends and googling around for cool open source projects, libraries and so. This, to me, is a good indicator - as long as you bring them up when discussing relevant problems, this means you thought about a problem and researched prior art to avoid re-inventing the wheel.
Also we tend to end up discussing pro and cons of any given technology and so on. This at the end is a key indicator you're talking to a passionate developer. And passion usually makes someone good at programming.
When it comes to soft skills, usually having such a kind of discussion you can figure out also someones behaviour in most work scenarios (to me, having a good "discussion" mode means you're likely to be fit for team work).