I did a podcast on DRS with Damith Samarakoon this week. You can hear it here.
These posts will help explain some of the points here.
On the Decision Stats published by ICC:
On the shift in "benefit of doubt" because of DRS - from the batsman getting the benefit of doubt, to the decision on the field getting the benefit of the doubt:
On the difference between an Error and a Mistakes
On Marginal Decisions after DRS