Its a pain for me too. I spend most of my time working from home, but I had the delivery date changing a few times and I can't install any software on my iMac until I get one without defects. So, its just used for surfing the web.
I agree about the QC issues. I think they seem poor. I mean what are the chances of having two defects out of two orders? Quite high it seems!
I hate returning anything. But when you spend over £2K on something, you want it defect free. I'm also thinking Apple might blacklist me for being a troublesome customer as I keep returning their stuff!