I use Internet Connection Sharing every day for work, and for the past several builds, when the screen turns off, ICS fails. I have found the following solutions fix this issue, and I hope one works for you guys too!
The issue is when screen turns off, some WiFi stuff happens and breaks ICS. The fix is kinda weird, but it makes sense when you know what's going on. You either need to delete all of your saved SSIDs, turn off Auto Connect on all of your WiFi SSIDs and turn off WifiSense, don't let the screen turn off by launching Maps, or turn the screen off then connect to your phone over Bluetooth and the have your device initialize WiFi sharing (screen never turns off because it was never on!)
Hope this helps!
The issue is when screen turns off, some WiFi stuff happens and breaks ICS. The fix is kinda weird, but it makes sense when you know what's going on. You either need to delete all of your saved SSIDs, turn off Auto Connect on all of your WiFi SSIDs and turn off WifiSense, don't let the screen turn off by launching Maps, or turn the screen off then connect to your phone over Bluetooth and the have your device initialize WiFi sharing (screen never turns off because it was never on!)
Hope this helps!