We covered this topic twice in the past, including January 2008 and December 2007. A post by Ben McKay has 80+ SEO Job Interview Questions, which may be the biggest list of questions I have seen to date.
I am not sure asking 80 questions to an interviewee is good. But clearly, have 80 questions you can ask and fine tune based on how the interview is going, is nice to have. Since we figure there is roughly 7% unemployment in the SEO industry, there are clearly talented SEOs out there looking for work. There are also many companies still hiring SEO talent, so getting the best talent should be key. Interviewing is just on step of that process.
There are many blog posts on the SEO interview, just see Google.
Forum discussion at Sphinn.