My DS seems to use his left arm more. When we hold him his left arm is pushing on our shoulders and his right just dangles. He uses his left arm when doing tummy time to start pushing up, and he is much more animated with his left hand. Both arms and hands work just fine, but I just notice he's using his left hand & arm more.                
                             
        
Re: Can you tell if your LO is a righty or a lefty?
Most babies start to show a preference round 6 to 9 months but you won't be able to tell if they are truly left or right handed until 2 or 3 years of age.
Natalie uses whatever hand is closest to the item she wants lol.
Even my 2 yr old does this still. Just when she strts showing a preferemce, the next week she switches.
I read that even young babies can show a preference for a particular hand. But it doesn't necessarily indicate handedness because they can prefer one hand for a few months, switch to the other, then use both equally, then switch back to one hand, etc.
That being said, Andrew prefers his left too! He has since birth...we'll see!
As a former preschool teacher, I will tell you that most kids don't "decide" their preference until 2ish, but I have had kids as old as 4 use both hands still (for writing/coloring/cutting).
Funny side story: I had one little boy tell his dad that "This hand is my at school hand (right) and this is my at home hand (left)." lol ) I don't know if he saw most of his friends using their right hand or what, but I thought that was pretty funny that he made that decision.
) I don't know if he saw most of his friends using their right hand or what, but I thought that was pretty funny that he made that decision. 
Matthew Kevin
7/31/83-7/20/11
Met 1/8/00
Engaged 4/21/06
Married 9/29/07
Two beautiful legacies: Noah Matthew (2 yrs) and Chloe Marcella (8 mos)
Day Three