When does eventually consistent really bite you in a user-facing system?

We often talk about eventual consistency as a trade-off for scalability, and that makes sense. But for user-facing apps, when has it actually caused big problems or a bad experience that made you wish you'd gone another way? I'm not just thinking about old data. Are there specific situations or features where it's just a no-go, and you absolutely need strong consistency, even if it means giving up a little performance or making things more complex?