Although I do not actively use Smalltalk, I check the Smalltalk blog feeds several times a week because Smalltalkers are often into interesting things. James has been talking about Smalltalk debuggers a lot recently.
While the state of Ruby debuggers is no where near those found in Squeak or VisualWorks Smalltalks, debugging controllers in Ruby on Rails web applications is fairly slick: in development mode code and RHTML templates are dynamically reloaded (CSS style sheets are not, but that is OK). The NetBeans Ruby environment with the "fast debugger" installed is pretty good. That said, I feel that Ruby has some big advantages over Smalltalk for some types of applications, so it is really a personal decision based on what development and deployment requirements are.
Using a debugger to step through how Rails controllers are called is also pretty interesting, if not educational.