"We’ve also incorporated into the core platform all the configuration files necessary to build the source code of Android Open-Source Project on its own. You can now build and boot a fully open-source system image out of the box, for the emulator, as well as for Dream (ADP1), Sapphire (ADP2), and Passion (Nexus One)."
I wonder how good it will run on the Dream (ADP1) though. Open Eclair was not much fun.
Open Eclair on Dream always had issues, partially because they never finished reverse-engineering all the closed-source drivers. CM5 on Dream has been quite nice for me; it can get a bit laggy sometimes, but beyond that has worked well.
It'll be interesting to see how Froyo's JIT fairs on Dream, for sure.
If you have unlocked your Nexus One (using "fastboot oem unlock") then you can build Froyo from AOSP and install it yourself (or you can download and install a build by someone else if you trust them).
If you do not want to unlock your phone, then you will need to wait for a signed OTA update from Google.
The AOSP build does not include any of the Google apps or frameworks (GMail, Google Maps/Navigation, Market...). You either need an official Google build for that, or you need to use one of the methods to copy those apps from a image that has them.
I'd really like tethering...