Minified JavaScript and CSS
JavaScripts and CSS should be minified for production use.
In Rails 3.1+ the asset pipeline will take care of this. Thus you're best off using an uncompressed version of your Javascript in development. Also load the non-minified versions of libraries. This way debugging will be easier and you will still get all the minification love once deployed.
In Rails 2.3 and 3.0 you should at least embed external JavaScript libraries in minified form, using something like JavaScript compressor.
makandra has been working exclusively with Ruby on Rails since 2007. Our laser focus on a single technology has made us a leader in this space.