Rosalind.info is a great project to learn Bioinformatics by solving programming challenges. The system is similar to the one you would find in the Google Code Jam in which you are given a problem and a sample input and output. When you think you have solved the problem, you are given a dataset to solve and you give the answer.
What makes Rosalind special to me is that I came across it a while after enabling a Rocks cluster at the university to run Bioinformatics problems using the Rocks bio roll. I never quite understood the kind of problems that it solved, what they mean and what the symbols represent. Rosalind is great in that sense, since it gives you the opportunity to just go straight to the coding part but also offers a brief background on the purpose of the algorithm you will have to implement.
I have solved only a few challenges, and due to a project that I am updating at the moment, I decided to solve the challenges using Python.
If you would like to learn about Bioinformatics and you enjoy programming, you should definitely go to Rosalind and check it out.