Take advantage of both processor cores when running tests:

Before DeepTest

$ rake test:functionals
(in /Users/dan/projects/thoughtworks/auction/)
Loaded suite /usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake/rake_test_loader
Started
[dots removed]
Finished in 211.975425 seconds.

962 tests, 1857 assertions, 0 failures, 0 errors

After DeepTest

$ rake deep_test:functionals
(in /Users/dan/projects/thoughtworks/auction/)
Loaded suite #<DeepTest::SupervisedTestSuite:0x4ce1e14>
Started
[dots removed]
Finished in 131.547951 seconds.

962 tests, 1857 assertions, 0 failures, 0 errors