Hurt users and discourage using that product. Imitation may be the sincerest form of flattery, but for Adobe Photoshop, imitation also means competition. One of the more serious competitors is Jasc's Paint Shop Pro 5.0. In previous versions it was just another also-ran, but the latest incarnation can compete seriously with the marketplace behemoth. Layers of Improvements PSP 5.0's most significant enhancement is the addition of layers, which allow you to build an image whose elements can exist independently of each other, as if each was on a transparent overlay.
Layers make it much easier to alter parts of an image without affecting the rest.
Version 5.0 also adds multiple levels of undo, with a helpful window that summarizes all the recent undo-able changes you've made. You can't undo changes out of the sequence in which they were made, but this Change History view does let you undo many changes at one time. Unfortunately, one thing you can't undo is an undo itself. There is no redo in Paint Shop Pro. PSP 5.0's output format support is also strong.