Well, I better grab any sheet on there worth saving in the case something does actually happen. Wouldn't want to miss out on tons of pieced together enemy sheets. ^.^
Well, both .jpg and .gif can be bad for sheets. .jpg, as everyone knows, compresses the image, and makes any kind of sprite unusable. .gif can sometimes cause color dithering. Is it possible to limit it only to .png uploads? (.bmp is known to eat up bandwidth like a bawss, so...)