Here's my reasoning...
I plan on purchasing the late-2012 iMac but am holding off for a few months.
The machine I will most likely purchase will be a BTO:
27" 3.2GHz i5
16GB RAM
1TB FUSION
GTX 675MX 1GB
My reasoning for holding off has everything to do with this being a new generation machine. Ideally, I would prefer to be in cycle to purchase the next iteration, but am imminently in need of a new machine, so the late-2012 will be my next computer.
However, I would like to see the lengthy shipping delays disappear, for one. When there is such a strong demand for a new generation along with published issues with the manufacturing of them (screen assembly in particular and potentially other parts), it concerns me. I'd like to see the machine out in the wild a little longer to see if any serious issues arise that require Apple to make adjustments to the assembly or production line processes. I'm also worried that the workers who assemble these gems are working fast and trying to meet launch deadlines and order demands, and in the process, rush the build quality. Something we saw with the iPhone 5 quality control issues.
Until the online store catches up to a more consistent schedule of 3-4 days of delivery time, I plan to hold off. This will be balanced or concurrent with keeping my ear to the ground to see if anyone has been having serious issues. It seems there has not been much noise with the earlier-released 21.5" version, but the 27" has only just begun to arrive in owners hands. I'd like to see what the overall feedback is with the 27" machine, before investing close to $3,000 on it, inclusive of AppleCare and state tax.
Other than that, I think the machine is fine, spec-wise. No complaints there.