There are no software limits on users. It all depends on what your hardware and connection can handle. The Groupon dev team helped us beta-test it a bit, and i

There are no software limits on users. It all depends on what your hardware and connection can handle. The Groupon dev team helped us beta-test it a bit, and it handles 100 users well with decent hardware on Apache (they were using an EC2 instance, though I am not sure what size). You could probably go up to around 300 or so without issues on Nginx and PHP-FPM, but I'm not sure you would be able to get to 1000 without adding memcache or load balancing. We are looking into making a pure node.js version with websockets if there is enough interest, though the price point for something like that would likely be higher. We are happy to provide support and additional feature development (like memcache integration) as needed. Just send us an email if you require anything custom, and we can work out the details.