One thing great about Slicehost is it’s DNS API. You can programmatically deploy new web sites. Save the need retype things field by field. And best of all it uses ActiveResource. It may seem lame but the reason why Ruby on Rails is installed in my computer is just because of ActiveResource. (It was just yesterday I really understand how ActiveResource work and that it is just REST being wrapped nicely and I can use PHP to do the same saving the Ruby learning.)
Cafyn wouldn’t be possible without Nginx, Apache, MySQL, PHP and WordPress.