It appears that Youtube no longer auto-rotates anymore. My assumption is that it has to do with rooting your device (I rooted to install the Gmail 4.2 leak) since this is the only major change I have intentionally made to the device.
Although even prior to the latest firmware updates, auto-rotation has always been hit or miss depending on the app, the alignment of the stars or God knows what else. It is a known bug that ICS has baseline issues with auto-rotation, which sucks if it is mounted in the car and a phone call comes in or you happen to try to pull up a notification at a traffic light. There are sensors in the device that seem to work 50% of the time when it comes to apps, but at its baseline level the OS shouldn't suffer these problems.
Has anyone else started to have rotation issues on YouTube??