Node.js has a lot of advantages, but you do have to know what you're doing to take advantage of it's power. That usually takes some time. The primary bonus against rails is that Node.js is more lightweight than Rails (which is saying a lot, IMO), and supports higher concurrency.
Though I feel I should side note at this point that a lot of real-time data retrieval doesn't necessarily mean you need high concurrency. It means that you need to make sure your middle tier and data access tier are very speedy, and that you can handle the throughput. By definition, Node.js covers the first one. Though either way you're talking in low milliseconds for response times.
If you want to get in to the JavaScript event-driven world, I'd certainly recommend trying it out. But for something that's not just a 'test it out' project (for your first attempt), I don't know how good of an idea it is.
Either way, best of luck!