Hi
Just before completing firmware upgrade with Kies to gingerbread, the screen of my Samsung Galaxy S turned blue and Kies went in to connecting mode, not finding the phone. After ten minutes, I concluded the firmware update had failed.
I disconnected the usb cable and the phone-connection-warning-signal-computer icon appeared.
I succeeded recovery of the firmware by:
1. Turning off the phone by holding down the power button until the screen turns off, and then immediately
2. push simultaniously volume down, start button (in the middle below the screen) and the power button, and thus bringing the phone in download mode again with the yellow picture of the android with shovel and text "downloading, do not turn off target!"
3. Because I had closed down Kies, I restarted Kies. If you don't close down Kies, restart might not be needed.
4. Reconnecting the usb cable, making instructions of Kies for emergency recovery of the firmware appear.
5. Click the button "Emergency recovery". In my case the firmware recovery was a succesfull update to the next version, Gingerbread.