I have played with the custom post types in WP 3.0 and it’s pretty fun. I have added a post type to my blog for food, specifically recipes. It makes for some nice functionality for a blogger to be able to add data that doesn’t necessarily go into your feed. Plus with added custom taxonomy I can create a matrix of data to cross reference later. For my Recipes, I am using tag like taxonomy to track ingredients. Check out my recipes page to see it working.
(updated) I have removed the custom post types from my blog, just to simplify things for my personal blogging.