Blogbody goes through the main differences between Java and Ruby in terms of web development:

Patrick Peak had some thoughts on a Rails presentation at the Denver Java Users Group (why is there no Ruby User Group to talk about this?). Namely, he comes to the conclusion that the main benefit Ruby brings to the table over Java is that the development workflow is simply code, alt-tab, reload browser. In Java, it is typically code, compile, package, deploy, alt-tab, reload browser.

That leads him to a long riff about how Java makes ground back up with better development tools, but he runs across the place where Smalltalk is a big win, and Ruby could be with a better environment:

While IDEA is doing great, the specifications like J2EE are not keeping pace, and as such the vendors implementing those specs are not keeping up either. Tomcat and Resin, while fast, still take several seconds to start up. Until the JVM allows for full class replacement, quick startup times are critically important.

Let me run through the process in a Smalltalk environment - wait, I don't need to - you can watch it here. To summarize, it's code, reload browser. Notice how all those middle steps just disappear? No restarting the application server, no need to repackage everything - you just stay right in the zone. This server is an example of that methodology, actually - I test against my test server as Wilkes demonstrated, and then I push the code to the server - and just load it on the fly. That load may involve shape changes to existing classes, including ones that are persisted (i.e., the domain classes for the posts). No problem - it's Smalltalk, so it just works.