A good test to see if interview questions are you are posing to a potential candidate are good ones is to allow the candidate to pose a similar number of interview questions to you. If they can also pose problems that by your own standards you should be able to answer, but aren't, then you are not doing it right (unless you yourself are not a fit for the position under consideration which may very well be because you are in a different position).

For some reason, some interviewers start with a belief that they are smarter than the candidate. While any reasonable person would feel that they do not fall in this category, think about how would you actually know if you do (this is not to say that you do fall in this category). The job of a good interviewer is as much to not reject a good candidate as it is to not accept a bad candidate; in both cases thinking of the position under consideration. If you start with this mindset, and by default subject yourself to as much doubt as you are subject the candidate to when her answer does not match your thinking, you are doing great.