This is of no concern to people who install Mac OS X on Apple-labelled computers, but for those of us who decide to exercise our rights as consumers by installing Mac OS X on non-Apple labelled computers should surely take notice: this practice is quite popular among netbook owners, such as the Dell Mini machines.
Reports of developer builds of Mac OS X 10.6.2 killing Atom support have been around for a while, but it's now pretty much confirmed. It turns out Apple has been meddling with the information related to processors, and one result of that is that machines with Atom processors are unable to boot Mac OS X.
This leaves Atom users with the following two options, an easy one and a hard one. The easy option is to simply stick with 10.6.1 for now; maybe a future update will reintroduce Atom support. Another, more involved option is to upgrade to 10.6.2, but use an older kernel, or maybe even a custom kernel with Atom support.
All this really doesn't surprise me. The Atom 330, the dual core desktop variant of the Atom line, was not properly supported from Mac OS X 10.5.7 and up; you had to turn off HyperThreading in the BIOS to even get Mac OS X to boot at all.
Of course, Apple has no obligation whatsoever to look out for Atom users, as the company does not ship this type of processor in any of its machines. If you run Mac OS X on a non-Apple labelled computer, then you know what the risks are. Just as much as you have the right to use the software in any way you deem fit, Apple has the right to alter its software in any way it deems fit.
In any case, if you run Mac OS X Snow Leopard on an Atom - you've been warned.