I bought a Desire HD from Carphone Warehouse for £500. Less than 28 days later I had to take it back because the power button was failing (collapsing in and sticking under the plastic surround when pressed). I got it swapped for another on Christmas Eve. I took that back yesterday because the earpiece speaker was faulty (rattling during a call).
Having totally lost faith with the DHD build quality and not trusting that the next one wouldn't fail (probably outside the 28 day return window), I cut my losses and was about to take a refund. But the store manager was just logging a stack of their first Nexus S delivery into stock. Given that I wanted a high-end Android and nothing else fits the bill, I took one (with a nearly £70 refund on the DHD price).
I have to say, with 24 hours use, I love it. The battery life is instantly and obviously better than the DHD and it looks great. I know some complain about it being 'plasticky', but as HTC couldn't deliver decent build quality with the DHD, this has suddenly become a good thing in my mind. It's straightforward and feels well made. It's great in the hand and just feels like a top-notch Android.
Thanks to Paul's work it's already rooted and running his custom ROM. All-in-all, at the new lower price I'd say it has a lot to recommend it. HTC have really let themselves down with stupid design decisions on the DHD (never trusted those battery and SIM/SD covers either). I loved it's power and versatility, but I never used Sense anyway, so I don't miss that.
Just my thoughts on the Nexus S. I don't think anyone who buys one will be disappointed.