Update: Thanks to a few readers, we've now got a direct link from Google's servers to update from EPE54B to FRF85.
Update 2: Tipster Christian R has sent us a picture of his T-Mobile-banded Nexus One with FRF85, apparently updated from Android 2.1 build ERE27. Has the T-Mobile rollout begun? Not for us, at least.
Update 3: And now we've got a direct link to download a FRF85 build that'll supposedly work for any Android build. We can safely say that it worked for us on a T-Mobile device with 2.1 / ERE27. Download from Google here, and if you need direction on how to do the update yourself, take a cue from our commenters. [Thanks, MRCUR and afinite]
Update 4: And now it's official. Keep an eye on that notification bar if you're itching for the OTA method. So that's one phone down, quite a few to go! [Thanks, cl]
[Thanks to everyone who sent this in]