Right now I'm learning a ton... Entropy, compression, functional programming, genetic algorithms and genetic programming, artificial neural networks, k-nn classification, clustering, Bayesian stuff... Just a ton of stuff to be really excited about! What's some neat stuff you guys have learned about?
On my own: Objective-C, iOS Development, Native Mobile Development, Object-Oriented Programming, Memory Management, Human & Mobile Computer Interaction
It's safe to assume that I am really excited about the mobile world. I still love my laptop and plan on building a desktop next year; but iOS, Android, and Windows RT fascinate me. It may sound weird, but I love watching how people interact with their mobile devices. I always ask people which apps they like, what phone they are using/want, and what they would like to have that DOESN'T EXIST. As a developer, I find it both intriguing and useful to know what others want out of the software that is accessible to them.
Other Interests: Idealistic Virtual Reality, The Economics of Bitcoins, Mobile Battery Efficiency
The reason is that Algorithmic Information Theory provides a unifying view. Not terribly practical, though, but neat.