I learn things which makes me curious, be it solving mathematical problems or writing a peice of code which makes one's life easier( or at least makes me think like that!).
From writing a "Hello world!" program in MS DOS to writing complex application which manages optical switches, learning was huge and amazing.
Interest lies on developing application which can scale no matter how much data it has to process,building large scale B2C applications just to experience the flavor of distributed systems(and trying something related to event based architecture)!