Basically, how much math background do you need to understand how category theory is applied to Haskell? If you already have mathematical maturity, can you jump right into it, or should you be familiar with certain subjects in algebra?
The first step is to learn category theory without regards to Haskell (and if you don't have it, Haskell without regards to category theory). A book such as Lawvere's Conceptual Mathematics is a good start. Awodey is also recommended, and Leinster's recent Basic Category Theory.