I am an algorithm developer using MATLAB in my day job.
After a long day of writing code, I like to come home and relax by...writing more code -- I've recently picked up writing Android apps as a hobby. After 30 years of constantly expanding computing power, it's fascinating to return to a restrictive environment where you not only need to be concerned about limited memory and processing power, but conserving battery charge as well.
My rusty Java skills make this hobby even more interesting, as does the switch back and forth between high-level MATLAB and lower-level Java.