[pagantomato]

This is an easier question to answer if you've ever worked on some open-ended research or problems where the path to the solution is just not known. Those sorts of problems seep into your dreams even when the last thing on your mind is work.

However, even if you aren't doing research, good answers are probably found in those scenarios where you are pushing the limits of some particular software framework. Anywhere you have to bend the rules or invent new rules just to accomplish something makes for a good interview story. How detailed you go in your answer depends on how entertained the guy on the other side of the table is.