We don't know what it fixes yet, but we've gotten some tips -- and we're now seeing it on xda-developers -- that Nexus S handsets in the field are getting blessed with their first software update, build GRH78 (up from GRH55) with an official version of 2.3.1. Not everyone has it yet (we don't on ours), so as usual, this would seem to be getting sent out on a rolling basis. Hang tight, owners!
[Thanks to everyone who sent this in]
Update: The full text of the update is "This system update from Google contains important bug fixes plus the latest version of Maps." It's 1.9MB -- so yeah, don't expect much!
Update 2: By the way, it appears that the "checkin" trick is actually working to force this update (it usually doesn't). Just dial *#*#checkin#*#* from the dialer and you should get the update notification. Have fun!