Update: We're not sure how this is being rolled out, as hardly anyone is seeing updates, but via Droidnytt we found a number of reports on Twitter that people are indeed seeing the update.
Update 2: Count us among the lucky few who just received the OTA Froyo update, to our original T-Mobile-based device.
Update 3: We've done some additional investigation, and as far as we can tell, Google is only updating review Nexus Ones that had been provided to the press -- not off-the-shelf phones. We'll stay on this and let you know more as soon as we do.
[Thanks to everyone who sent this in]