Not all manufacturers have updated to Android 2.2 yet (and for some phones it will never come), but there is already Android 2.2.1 for the Nexus One. The small jump in the version number makes it clear: not much has changed. The Linux kernel has received a minor update, a wifi bug has been fixed, and there is a new version of Gmail.
As always, the update will be distributed "over-the-air", so it will not reach all Nexus One owners at the same time. Another obstacle: only devices purchased directly from Google will be provided with the update. Those who bought their Nexus One from Vodafone, for example, will not get Android 2.2.1 yet.