IssueTracker

Use an alternative home launcher.

Using the  stock 2.3 launcher this happens..there is also times when the screen will not scroll and only will scroll once the phone is rebooted..

Got my Nexus S today from the Carphonewarhouse.  Phone updated to 2.3.1 and after having it plugged in I added two email accounts.  When I returned to the home screen via the 'home' button I have the same issue as the OP.  A reboot was the only way to resolve this.

I am also having this issue but it did not happen until I deleted an app that was on the home screen.

I have also encountered this problem many times. I had to restart the device to be able to drag and drop again.

I am having the same problem on the Nexus S.  When I have the problem, I have to reboot the phone.  Then when I reboot it, I sometimes find these icons that went missing in one of the created folders (even though I never dragged it to any folders).  I am also usually unable to move folders into a different location without fully shutting down and rebooting the phone.  It will work after a fresh reboot but very quickly start to experience the same issue again.  The only way I have been able to get icons where I want them in some cases is to long hold the desktop where I want to set it and create the shortcut manually there.  Opening up the "all applications" menu and dragging to the desktop fails to work unless it is freshly rebooted.  Sounds like another Nexus S bug.

Try to kill the launcher and not restarting the phone it works for me

@shahamk what do you mean by "kill the launcher", these are unrooted phones running stock android on the Nexus S.

Unrooted too
Goto setting->application settings->running services->choose all (top of the screen)
Find 'launcher' and press on it
Press force stop

This should fix the problem like restart does
I created a shortcut to running services on my home screen but I'm not if this is an option of one of my many installed apps :-)