I know, i'm a loser for not having an iphone 4 yet, but what would happen if i copy this file to my 3GS and rename it icon.png (or whatever the name is) and respring? Would it look sharper on my 3GS, or would it not even be worth the hassle?
Unless you have a retina display on your iphone it wont make any difference than the one you have now.