Custom post types are amazing. Prior to Wordpress 3.0 (or maybe it was 2.7... can't remember), if you wanted to use post-like functionality for anything other than blog posts, you would typically do it by creating a bunch of post categories and use the cumbersome custom fields feature to add extra meta data. You would then have to modify your themes to display the posts in a different fashion depending on what categories they had been assigned to.
I use them all the time with my client projects. Some examples have included a business directory like what you're seeking, events calendar, products database etc. It's CPTs that have basically turned Wordpress into a full-blown CMS rather than just a glorified blogging platform.
Read up on CPTs in more depth at the Wordpress Codex.... (bit techie over there... but worth a look anyway). Post Types WordPress Codex