Hand signals are for wussies. I use the flare gun method. Yellow for left turn, green for right, and red for stop. It seems to work pretty good, as once I start firing away drivers always back off or yield.

Yes, I signal with my left arm for stops and turns. It's easier for me to do and motorists tend to notice it better.

A cyclist has the benefit of having both hands visible, therefore a straight hand out on either side is acceptable to signal a turn. For stops, I think a turn signal indicates that you are slowing.