If you switch to Rails 3 and Ruby 1.9.2 (or 1.9.1) you will get the error

Uncaught exception: no such file to load -- script/server

a simle edit of rvm/gems/ruby-1.9.2-p0/gems/ruby-debug-ide19-0.4.12/lib/ruby-debug-ide.rb will help

Replace the line 123

bt = debug_load(Debugger::PROG_SCRIPT, options.stop, options.load_mode)

with the following code:

if Debugger::PROG_SCRIPT.match(/script\/server/)
p_script = './script/server'
p_script = Debugger::PROG_SCRIPT
bt = debug_load(p_script, options.stop, options.load_mode)