I wrote a similar article trying to segregate hosting stages (though beware I'm a hosting company promoting a product) - http://blog.bytemark.co.uk/2011/11/03/t

I wrote a similar article trying to segregate hosting stages (though beware I'm a hosting company promoting a product) - http://blog.bytemark.co.uk/2011/11/03/the-cloud-is-your-install-script http://blog.bytemark.co.uk/2011/11/03/the-cloud-is-your-inst... . tl;dr version is that I think the ultimate flexibility is in your application's install script. If you can deploy to one host, or several, and collapse or split out caching layers, databases etc. depending on resources available, you have a truly portable application that's ready to scale and/or move ISPs.