This information alone paints a somewhat clearer picture of what's going on here. That the device will only be supporting T-Mobile's 3G network makes sense, as Google has favored T-Mobile with its Android strategy to-date. The Google Phone -- which is a complete misnomer, by the way -- will NOT work with AT&T's 3G network.
Google employees have published pictures of the device on Twitter, so we know what it looks like. It is a large, slab of a phone that has four capacitive buttons at the bottom of the screen (similar to the Motorola Droid and HTC Eris), and trackball for on-screen navigation. Given the sheer number of independent pictures of the device published, I believe we can say with authority that this is what the phone looks like.
Those pictures also reveal that it is running Android OS 2.1.
These are all the facts at this point. Everything else is speculation.
The Wall Street Journal says that Google plans to sell the device, unlocked, straight to consumers. Google has not confirmed that. Price points are all over the place. Don't believe any of them.
Others report that it has a 1GHz Snapdragon processor inside (because the phone looks so much like the HTC Passion). This is simply not known to be true.
The only details that Google has verified are that the device is being tested by employees over the holiday season.
Until Google, HTC, and T-Mobile offer more concrete details, we can only assume that the Nexus One is simply an unannounced Android phone.