<p>Do you have any examples of real life applications of mutation testing? Does it work better than simple test coverage tools? Or is it useless?</p>

<p>What are the advantages/disadvantages of mutation testing in the real world?</p>

I looked at mutation test some time ago as a method for checking the efficacy of my automated regression testing scripts.  Basically, a number of these scripts had missing checkpoints, so while they were exercising the application being tested correctly, they weren't verifying the results against the baseline data.  I found that a far simpler method than changing the code was to write another application to introduce modifications to a copy of the baseline, and re-run the tests against the modified baseline.  In this scenario, any test that passed was either faulty or incomplete.
This is not genuine mutation testing, but a method that uses a similar paradigm to test the efficacy of test scripts.  It is simple enough to implement, and IMO does a good job.