If you haven't had a chance to mull over Heroku's architecture, I'd suggest giving it a look. http://heroku.com/how/architecture

Basically, nginx fronts a bunch of Varnish caches, which are then in front of a "routing mesh", which queues up requests for individual "dynos". A dyno is a single-threaded instance of your application. When one dies or is migrated, another is deployed in its place. Multiple dynos are automatically spread across multiple machines. It's a very neat solution to automatically scaling hundreds or thousands of apps.

In other words, bundling the apps and pushing them out is just the beginning of a pretty fascinating architecture.