I'm also having the "not working" issue. I've had Internet Sharing work in the past but there has been a few times, like today, where I go in to the settings to start Internet Sharing (I use a modem dongle, so my Internet is not always up and running), the Wifi icon in the bar gets replaced by the Sharing icon for a half second, then it goes back to just being Wifi and starts scanning for Wifi connections. It's pretty frustrating, the data signal out here is weak on my phone so I'd like to be able for my phone to use the dongle via Wifi. It worked before.

I'm just trying to figure out what changed from yesterday to today, other than my MBP going to sleep over night.

I'm also having the "not working" issue. I've had Internet Sharing work in the past but there has been a few times, like today, where I go in to the settings to start Internet Sharing (I use a modem dongle, so my Internet is not always up and running), the Wifi icon in the bar gets replaced by the Sharing icon for a half second, then it goes back to just being Wifi and starts scanning for Wifi connections. It's pretty frustrating, the data signal out here is weak on my phone so I'd like to be able for my phone to use the dongle via Wifi. It worked before.

I was unable figure out what changed from yesterday to today, other than my MBP going to sleep over night. The good news is a reboot fixed my issue so perhaps this is something that can get wedged and needs a reboot to recover from the failure.