How scalable is one web server?

this is obviously entirely dependent on the kind of software you're writing. if all you're doing is serving static pages, sure, one server can serve a million or more requests a day. but if you have a heavy server side component, like handling large file transfers, or even extensive batch processing, you're going to hit a wall a whole lot sooner.

a simple, effective approach to this problem is to partition your site into services, each of which run independently. then, when it comes time to scale, you can scale each service to its own box and beyond independently, with the added benefit of minimizing downtime to a small sub section of your site.

I found the thoughts for the second question, "Should I launch a private beta?" to be more useful. I've been going back and forth over doing a private beta. I don't think that a hard limit for the initial userbase is always the right answer. It may be fine for services that are inherently single user but for social apps would you want it to grow virally based who someone is willing to invite?

Weebly is becoming a proof of concept. That you can withstand pressures of companies like Google when you outperform their own similar products.