Bump.
Interestingly, I was once at a shmuess from the Birchas Avraham zatzal, and he spent a good ten minutes complaining about how "those American bochurim" come to his yeshiva with short sleeves and how tznius is based on the minhag hamakom, which is not short-sleeves. Meanwhile, I was yanking down my jacket sleeves to make sure no one could see that I was wearing short sleeves.
Meanwhile, it seemed to me to be more of an Israeli thing among the yeshivish, and practically (but not entirely) unheard of in the states. That was then; I think the ratio is the same everywhere now...
Btw, I don't own any long sleeve shirts, and have not worn 'em since I was seven and decided I wouldn't. You can ask
@yfr bachur - he knows me since I was ten, at least.