Snapseed just updated on my iPad tells me it is now “retina display” optimised (well that’s for the new iPad, not my model, of course). But, it also now lets you port your photos directly into Instagram for sharing on that photo network, which is also nice.
I use SnapSeed a lot and have recently rediscovered Instagram (link is to my InstaGrid gallery) although I posted my first photo there some time in 2011…my latest favourite, fun photo editing tool is PicMonkey, which replaces/displaces PicNik (about to be subsumed into Google+ photo editing, I believe).