Yeah, I had this problem until I figured out what was going on.

If you're using an x-10 universal remote, you may be nudging the POWER button. I found that sometimes all the lights would just turn on, because I was bumping the power button, or rolling over onto it (in bed ... I LOVE my X-10), or otherwise causing the problem myself.

The X-10 key is usually the LAST one I hit before going off to bed. If I don't remember to hit the TV button again, I will occasionally hit that Power button. Whoops.