I can confirm two of these.
#1 is the for whatever reason the game cuts the center channel completely. I had a buddy over and he was using my 5.1 headset and I was using my Dolby 5.1 surround sound. Around every hour or two the center channel would go completely quiet. Had to go back to 360 dashboard and start the game back up to correct it. This explains vehicles becoming almost completely silent as well as any audio that would be sent through the center channel.
It's not the console hardware either his is an old first gen second revision and my 360 is a slim second revision. Also I was getting my optical out directly from my 360 and he was getting his from the AV VGA cable.
#2 Is not being able to take human shields after 30 minutes to two hours. This is also other Y button related bugs and issues. Brutes not being able to be taken down and some others that have been mentioned.
A third one that I haven't seen mentioned is a weird bug that we had playing co-op. If some condition was met when you were calling up someone and the other player died or got a mission checkpoint you would be stuck looking at the phones calling list. Only fix was to go to dashboard.
Another odd bug was that after awhile he could see the enemy gang, but not the gang wipe icon on the mini-map or the icons that appear over their head when you start it. While I could see them fine. We both started the game from the beginning in system link. After about six hours this started and it didn't matter who was the host I could see them, but he couldn't.