What are examples of innovative uses for custom fields?

I was recently hired to redesign a huge WordPress-based website. Each one of its several post types will have its own custom fields, which is making me think “How the hell will I provide this client the most automated and simple experience I can design to create all these kinds of posts and related name-value pairs (e.g. time and date of events, name of artists on a certain festival)?”.

This is why I’d like to know examples of good, innovative and interesting uses for custom fields. In my case, I’m using them on my personal website to enable social media and sharing independently for each posts (e.g. each post has its own Flickr, Dribbble and Behance pages). In a nutshell, I’d like to know the state of the art for the uses of custom fields in content-rich WordPress websites. How are you guys using the custom fields on your themes?

Pardon me for my rusty english.