The benefit that Photoshop has is familiarity and Adobe's pricing structure is that of an abusive monopoly - they know they can charge as much as they do because they have a monopoly. This monopoly was earned in large part because early on, Photoshop was the most accessible app.round about 5.0 Adobe started to get sloppy.

I've started using Pixelmator for about half the image work I do on the Mac and IMHO it represents excellent value for money. It works like Photoshop used to do. It's lacking some feature, mainly the ability to work in colour channels, but for the price, it's hard to beat.