They teach Java in the intro level courses so they tend to stick with that later because they can expect the students to know it. If you're interested in why I don't like Java much, here is a good explanation. Don't take the title "Why I hate Java" too seriously. It's just a good summary of why I prefer C/C++.
I enjoy working with graphics and games. One of my favorite libraries is SDL.
I am interested in the Hurd and would like to contribute if I can figure out the best way to. I have gotten it running and played with it a little but it can be a slow and exhausting experience.
I wrote a tutorial on writing a kernel from scratch in C for a senior project. I ran out of time as I was really getting going porting newlib I would have loved to get some GNU software like bash to run. I may have gotten GNU hello to run. Writing a compiler might be fun as well. I've written an assembler and linker for a toy virtual machine in class and got interested in compilers a little.