Some time ago I had the chance to work wuth a development team which had separate QA resource. The team was working in the standard "over the wall" mentality. Developers do stuff, QA engineers pick it apart and so on.
I heard a phrase which really gave me pause:
"QA is working on behalf of the customer"
This sounds great, the QA engineers really take ownership of thinking about the customer. What does it say about the development team motives? Aren't they thinking about the customer?
In the teams I have helped shape I have always avoided dedicated QA because I suspect it creates an environment where people defer responsibility. On the other hand it might mean that a stretched development team can roll out faster as they can rely on QA to catch the issues. That might sound plausible but in the world of ever accelerating deployment can manual testing really keep up?