I've used Photoshop for years, and recently upgraded to Photoshop CS5 mainly for one feature called Content-Aware Fill. It allows you to remove an element from an image, and the software very cleverly fills it in based on what is around the deleted object. It's quite amazing to use, and I'm often calling it up for landscape photos when an errant tourist or power line gets in the way of what would otherwise be a nice image.
If you're not about to shell out several hundred for Photoshop, or almost a hundred for Photoshop Elements which has a similar feature, let me direct your attention to inPaint in the Mac app store. This US $9.95 app (on sale for about a week for $5.00) has this same feature, and if removal of some parts of an image is what you really want it's worth the small price asked.
Here's how it works: You open an image in inPaint. You use a brush tool to paint out the object you want removed, then you hit a 'play' button to start the repair. The brush tool can be varied in size, and you can brush away multiple unconnected objects in one operation.
I tried inPaint on a variety of images, and compared how it did to Photoshop CS5 content-aware fill. In some cases, inPaint removed the object with fewer steps and left no evidence it had been used, where Photoshop left the image looking a big ragged. In other cases, the two applications worked about the same, but in none of my experiments did Photoshop do a superior job.
inPaint is not a substitute for a high-end editor. No layers, no sharpening, nothing really except the ability to smoothly remove parts of an image without a trace.
One drawback is the app can't open raw files. The developer says that is coming. I had no trouble opening TIF, JPEG or PNG format images.
Photoshop is a terrific app. I use it every day. It is versatile, and does everything a graphic artist or photographer would want. However, if you are looking only for the ability to smoothly remove unwanted things in your image, inPaint does it extraordinarily well at an almost microscopic price. I have some examples of the app and a Photoshop CS5 comparison in the gallery.