If you’re in a hiring phase you’ll want to peruse Aaron Swartz’s thoughts on hiring programmers. The process that he walks through could, and should, be used for hiring just about anyone (not just programmers).
However, I would add one step to the beginning of the process. Watching that person online. I know it seems kind of stalker-ish but on today’s Web many people Twitter, Facebook, or MySpace what they’re doing and by that you can usually tell if you even want to begin this ‘casual non-interview-like interview process’.
For instance, some people are overwhelmingly negative Twitterers. I’d never hire an overly negative person. Some people Twitter that they love the latest version of Windows – I’d probably never hire them either (kidding, sorta). Others may constantly share the stuff they are working on, or they blog a lot, or they share some of their interests like music, food, or their favorite books. These are the people I’d "interview".
You get the idea. Become a stalker and you might save some time.