These are new leaves that have opened up either spliting or have holes in them. I have five or six trees that these new leaves have appeared on.

Check at night for caterpillars or beetles.

I believe there are some very small things that can infest a tree and cause this also.  (i.e. bacteria or some other microorganisms).  I've seen things that looked similar before on a couple of trees I bought.  (On my trees) that problem went away as the season progressed and they got a flush of newer growth.  Not sure it's the same thing though.

Mike

I would wait until night hours and then check the underside of the leaves for starters. I have seen some plants where it's just genetics but they usually all have the same deformation or hole in the same spot on the leaf. I don't think that's the case with this one. Those holes like they were dinner for something.

nuh... I thing those are the first leaf of each branch, when they were baby they protected the growing tip, so they got some damages growing up... that's my opinion. Those holes look healed and never bothered again and again.

i agree with aaron on this one. i used to think it was some sort of FMV. then about few weeks ago, i kinda sorta "pushed" against the terminal bud on my Salce while aerating one of the bigger trees. it leaked latex and all that, but i didn't remove the bud. now it's putting out leaves, but they are all misshapen. i think some of the buds take some damage during the winter storage and it shows on the new growth. after awhile, the new leaves will look just fine. 

Looks like what i have on several trees that were just starting to leaf out and got a light frost a few weeks ago. Were yours outside during a recent frost?