Google Nexus S, google's second handset is in the limelight for wrong reasons this time. Looks like, the nexus S handsets are randomly rebooting atleast once every 48 hours, usually during a voice call! Google has officially confirmed this bug in their support forum. All the handsets that has been updated to the latest version of gingerbread (Android 2.3.1/GRH78) are affected by this bug.
Google engineer officially confirmed this and they are currently investigating the problem in association with samsung. This is what he had to say "So we've successfully reproduced this issue and are in the process of investigating with Samsung. I'll provide updates as soon as I have them."
Evidences are pointing that the bug might be due to the Operating system and not related to hardware. This bug appears only on the handsets which has upgraded the os to 2.3.1. When some users tried to restore to factory settings, the bug seems to have died down.
Official fix/patch is still awaited. While google nexus handsets enjoy the possibility of getting frequent android updates, sometimes the users have to pay the price in the form of bugs :)
Via Google support forum