Fantastic. Pusher is an awesome product that eliminates the headaches associated with building a real-time product. I'll never build a chat with polling again. I use it for my website and haven't had any problems (well one, but it was mostly caused by my inexperience with rails)

The best part is the pricing, especially for startups. 20 concurrent users for free is a big number. Compare it to something like MailGun, and it seems like $20/month gets you a lot more value.