When I got home yesterday my iPad 2 was locked to sideways orientation. No, it wasn't the mute switch. That feature was set to control mute and just in case I switched it back and forth and it made no difference (both the setting and the actual switch). I thought maybe the accelerometer or the gyro was defective. I went into settings and did a reset of all settings, and that fixed it.
Any idea what happened? Is there some orientation lock feature that you can activate accidentally?