It seemed, upon analysis, that high-profile bloggers and journalists that had gotten pre-release Nexus Ones were receiving the update early. Once again, many are on high alert, as TechCrunch, who raised the alarm earlier, says Google has confirmed to them that Froyo is rolling out to Nexus Ones.
It's true, also, that those who can't wait for the update come OTA can get it manually. That only applies, at least for now, to those on stock (non-rooted) ERE27 ROMs (meaning the version released that covers T-Mobile 3G frequencies, not the later version of HW that covers AT&T 3G frequencies).
In addition to a 250 - 450 percent speed increase (benchmarked), there is 10.1 Flash support, wi-fi tethering, and a lot, lot more in this release. It is a good move on Google's part (assuming this isn't a false alarm like last time) to get this out before Apple's fourth-generation iPhone announcement.
Update: nope, despite the assurances of TechCrunch, it's another false alarm. In fact, it was as originally thought, an early build released to journalists. Not only that, it's not even the final build.