Back at the beginning of September the Samsung-made Google Nexus S received an Android 2.3.6 update but caused some issues (with WiFi and USB tethering) and was quickly pulled. The Nexus One successfully received the 2.3.6 refresh recently and now the Nexus S is getting the update rolled-out again.
The new update is build GRK39F (opposed to the buggy one which was GRK39C) and is still Android 2.3.6, with reportedly working tethering functionality. If you know your way around updating and playing with ROMs (insert usual warning here), head over to the source link to download the update file (GRK39F-from-GRJ22). It appears that you already have to be on GRJ22 in order for this to work.