Whenever I start a new Rails project, one of the first things I do is install Rspec and delete the Rails default test directory. Even with that directory missing, however, Rails continues to waste my time by trying to run its various testing tasks.
To make it stop, just add the following:
Rake::Task[:default].prerequisites.clear task :default => :spec
to the bottom of the Rakefile in the root application directory.
Obviously, if you want to have a default task other than spec, just change the right side of the second line to whatever task you want it to run.