IMO, whiteboarding is only a part of the interview process. Probe their breadth and depth of knowledge relevant to the expertise you seek (for instance, if you were seeking an expert in databases, ask about pros and cons of various data stores, search, RESTful access, scaling), look at community (online/offline) presence (Github, HN, LinkedIn connections, Tweets, Klout, Meetups, etc.), agility (since you're probably a startup - simple stuff like how fast they type or how efficient they're with the keyboard and mouse together), etc.<p>Most of all, if you don't feel that they're smarter than you, they're probably not right...