Interesting to see Perl used at Microsoft:
Our main deliverable is our test suite. Our last test run consisted of 18,697 tests. Each test is pretty much a full program that we compile and either execute and verify we get the expected results or verify that the compilation failed for the expected reasons.
One key attribute of our tests is that they're all automated. We write a test, check it into our source control system, and it will run forever without any more user intervention. We don't do any manual testing at all, and we intend to keep it that way. Our test harness (tool we use to execute and validate results of each test) is a Perl script developed several years ago, before C#, in the C++ team (which is where the C# team was born before we had our own product unit) that has proven to a lot of us that simple is often better when it comes to test harnesses.