I've flown with mine through SAN and LAX and on no occasion have I had to take it out of the bag. The only time they gave it a second look is when I added some girl scout cookies to the bag.

I carry a letter with me that says that my CPAP machine needs to travel with me in the cabin. I've never needed it but, it should help with being able to take it in the cabin if a over-zealous check in agent causes a fuss.

I always put mine in the overhead bins. It's not very big and doesn't take up a lot of space.