Add AFNetworking to your project (eg. via cocoapods.org), copy these two files into your project, then
#import UIImageView+AFNetworkingFadeInAdditions.h
and use it like this:
[imageView setImageWithURL:myNSURL placeholderImage:someUIImageOrNil fadeInWithDuration:0.2f];
Will be using this in our Shindig app. Thanks very much for the contribution.