Sure, the Rails error pages are ok.
They explain whats going on but its almost an art form to properly understand what happened, ok maybe not an art form but they could be better.
Better Errors is a replacement for the standard error pages of Rails and it will also work in your rack apps with a bit of configuration.
Setting up with Rails is as easy as adding the following to your Gemfile.
group :development do
Next time you generate an error, and really how often does that happen, Better Errors will display a better error page.