I have been using the fine Dojo Javascript library in a web app written in Common Lisp and this morning added Dojo to the code base for a current Rails project. The easiest way to get started using Dojo and Rails is to simply install the developer's version (non-compacted) of dojo.js and the src directory directly in your Rail project's public/javascripts directory, so it looks like this:
Again, the "src" directory contains the dojo source files (besides the dojo.js loader). Dojo will complain about rendered Rails web pages withot HTML and HEAD tags, so I added the following HTML with Dojo setup to the view for my main application controller:
  <title>KBSportal KnowledgeManagement</title>
  <script type="text/javascript">
  djConfig = {isDebug: true};
 <script src="/javascripts/dojo.js" type="text/javascript"></script>
 <script type="text/javascript">
 <style type="text/css">
  body {
   font-family : sans-serif;
  .dojoTabPaneWrapper {
   padding : 10px 10px 10px 10px;
Dojo is definitely "heavier weight" than the prototype.js Javascript library that is provided with Rails so you may not want to use Dojo for very high traffic sites.