I like the pattern these escalator steps (Hilldale target store, Madison) make, especially side by side, but this abstract diptych is really intended to illustrate a point. I tried several photo editing apps this afternoon, trying to find one with a clone stamp I could use on my iPhone. A couple of apps, PhotoForge and Photogene, both have a lot of bells and whistles and used to have clone stamps, but their current versions for the iPhone no longer do (don't know about iPad). Then I tried Filterstorm. It has a full range of features, including macros, masks and layers, but it also has a very useful clone stamp that is implemented elegantly in the small surface area of the iPhone screen.
I decided to use the image on the left as a quick test. There's little documentation that I could find, but the interface is pretty intuitive, and within five minutes of downloading the app I had used the clone stamp to take out an easy target -- the bit of yellow at lower left. You can zoom in for detailed work, so I assume I could use Filterstorm for more challenging situations as well. In addition, Filterstorm will work with and export high-res images (like panoramas, for example...)
Now I really do feel I have a photo editing studio in my pocket. Whether I need it is another question, but it's nice to have it.