There are also some other filters such as the soft vignette that look neat, but the rainbow filter that modifies all the colors on your image so that it looks like a rainbow is a little odd. I suppose my 5 year old would think it was pretty cool.
Anyway, it looks like a neat app. You can send your images to Photoshop.com, or save them back locally. The app creates a new image at the end of your camera roll, so your original picture is not changed. You can choose to take a picture right from the app too.
It is free, and looks like it is worth playing with a bit. Search the app store for Photoshop.com.