the animation in the tree is smooth as it should be, kudos for that, as it's more simple than i looks. however, I see that clouds's animation is sloopy. i would suggest you a few points:
>reduce the speed of the clouds(only the cloud, not the branch) and to fix their movement. a one pixel movement per frame at 12/100 would surely look more fluid and nicer rather than the 2px-3px you made at 0/100 -the frame delay 0 doesn't exist! =D)
>if those yellow  points over the clouds are supposed to be ligth, they shouldn't move with the clouds. that's ilogic since they re fixed. also, they re almost invisible withut zooming at least 2x. fix 'em or remove 'em.
>some sutile color changes in the leaf would also give it a more natural look. as it moves, its shadows should change too. if you want to get complicated, the ligth of the leaf (and of the entire image) should be afected when the clouds pass over the sun. if the sun is the ligth source, when a cloud covers it the global brigth of the image should decrease gradually untill it gets uncovered again (it could never be 100%, its not an eclipse, the ligth still pass thru the clouds).

this is a good animation. hope that you would give it a few more minutes to fix those points and make an exelent animation.

Yeah I know what you mean

I think what nightmare meant was they all move as a group, although all clouds dont move at the same speed naturarlly. If so, then i second that.

look, the frames are very detailed, but I just think that the clouds are too "stone", they just go to the right, without moving between them

hope you understand what I am saying =P

Mighty fine