I regret switching my tribe to X2 speed and then going to sleep, thinking I had paused the game. Fortunately, I checked on the tribe the next morning so it wasn't too bad, but it messed up my Esteemed Elders and Breeding programs! I had to work extra hard to make up for it.

I still use X2 at times, but now I double check that the game is actually paused when I want it paused.