Fast vs Slow – anyone?

I've been hearing folks lately label themselves as "fast" or "slow" writers, with regards to their annual output of publishable work. I must admit that I have no idea what the criteria for these labels are. As someone who lives and breathes the labelling of the human race (if I could, I'd label gun each and every one of you), I must know what the definitions are for both fast and slow writers.

I am disappointed at my 2010 output, for example. It was a huge year of changes in my personal life and significant adjustments all around. However, does that mean I'm a slow writer or that I just had a crummy year?

Therefore, I call upon all of you to help me label myself. What makes a person a slow or a fast writer?