Honestly, I think that a grid view of categories is not a great idea from a usability point of view… it adds just one more click for the user. Once they get to the product grid/list page, they are going to have the horizontal or vertical text nav anyway.
However… a category overview page with cat. image, cat. description and maybe five teaser products per category might be cool.
Short: let me finish the stuff I need, then I will see about the category ideas.