Now the folks at Nik Software are at it again. They brought snapseed to the Mac in 2011 and it is available in the App Store for $19.99. Take a look at the video here (and at snapseed's website) and I think you will see why it won Apple's app of the year and why so many people don't have any other editor on their iOS device.
I am a huge fan of Pixelmator as my photoshop replacement for my Mac, but I think for the quick and artsy touchup, snapseed will be my new go to app. And with Flickr & Facebook functionality built-in to the app, you will be able to share your work easily.
A quick note for Android users... their web site says "comming soon" ;-)