Some Samsung Nexus S owners are seeing Android 2.3.6 roll out to their devices. We say some, because not all devices and not all carriers appear to be supported as of yet, though Google states the update will be rolled out over time and in some cases -- depend on carrier approval.
Sprint has an update, GWK15F, posted on their site while folks in Canada on Rogers and Fido are also seeing an update marked as being GRK39C. Mysteriously missing though is anyone getting updates on a T-Mobile or AT&T Nexus S. The update is said to correct a voice search bug, but at the same time, its been confirmed to also break WiFi and USB tethering across all devices which have thus far received the update.
All rather strange, really. If you get the update notification however, you may wish to consider putting it off until some more info is gathered up about what, exactly is going on with it. That said; if you got the update then by all means -- let us know in the Android Central forums so we can get some clarification happening for others.