4.2 on my Nexus 7 is really, really slow. Also find the power button to be unresponsive at the best of times. Often have to press it several times before it switches on. Could well be that that's related to the slowness!
Tried to buy a 16gb Nexus 4... failed miserably. Furthest I could get was to the payment confirmation page,at which point it told me that my credit cards were expired (they're not, I frequently use them on the Play store !). After re-entering the details it fell over with server errors again... then, as quick as they had appeared, they were back to "Coming Soon".
I do wonder if they've only allocated small stock to each country for the launch, to make them "sell out" in each country... then after it's launched, release a load more?