Count me in as one having YouTube issues, too. New Hopper 3 installed 12/2. YT worked fine that day. 3 days later, I get the red splash screen for a few seconds, then black, and the Hopper 3 reboots itself about 3 times. Tried resetting YouTube to defaults but no luck here. After the 3rd reboot and Starting Up splash screen I get a small window in bottom right corner saying "Please Wait, Refresh in Progress, 9999" and then it eventually goes to live TV or turns off and I can power it up and watch TV.
Also having an issue with Pandora. It logs me in and starts playing a station but no audio and plays maybe 3-4 seconds of a song then skips ahead, and keeps doing this, even skips passed commercials like this. Looks like some software fixes are needed for Apps.