These pre-beta builds, which I will collectively call build 69xx, are for pre-beta builds both very (very) stable and close to being feature complete. I've been running these builds on a few machines now for a total of a few hundred hours and I've not had a single crash or hang, although the test systems didn't like the preview driver package for the ATI graphics cards.
Given what I'm seeing now I'm expecting a beta in January and for Windows 7 to go RTM earlier rather than later in 2009. These 69xx builds, unlike the 6801 build that was given out to PDC attendees, have none of the hidden "Blue Badge" features. Everything in these builds is on show.
There's not a lot new in these latest builds. In fact, I don't expect to see anything potentially "special" until the beta comes out (which in my opinion will be more of a release candidate). The 69xx builds are about getting the core OS right, and my testing suggests that Microsoft is getting things right this time. These 69xx builds look and feel better than the RTM version of Vista did.
The new Task Bar does take a little getting used to, and is more of a jolt to the system than seeing the Ribbon UI in non-Office apps is. I can see this feature dividing users into "Love it" and "Hate it" camps almost instantly. I initially hated it, but now feel that it is an improvement over the Vista task bar, but I feel that it still has that feel of being "mystery meat." For example, take a look at the image below and tell me which are running apps, which running apps have multiple instances running, and which are shortcuts?
A feature that I like a lot is Aero Snap. This is a gestures driven method of organizing Windows. Drag a window to the top of the screen and the app is maximized. Drag it to the side and you get it to tile to one half of the screen. Drag the app away from the top of the screen to restore it.
Also new are Jump Lists on the Start menu. Keep your eye on the Getting Started entry at the top of the list and see what happens when I hover over it: