GIMP certainly does a lot more when running on Linux than Photoshop does - given that Photoshop will not run at all on those systems. GIMP also supports a lot of add-ons similar to some of the ones that can be run on Photoshop.
You wouldn't expect a free program to do what one of the most expensive ones can do anyway and for what you pay for it GIMP does lots more than Photoshop does for each dollar you spend..
Although I do use Photoshop more than GIMP now when I was only running a Linux machine I could only use the latter (as felgall mentioned). I found it a more than adequate replacement for my needs especially when taking into account the cost (free) compared with Photoshop. On this basis, for me and my requirements there is only one winner.
I used Photoshop for years and years, professionally, in art school, for fun.
Here's the answer: The serious work you do in Photoshop is color correction and selections. GIMP has all the same color correction tools and all the same selection tools as Photoshop. You master color correction and selections and that's it, if you want to get more advanced, study composition, color modulation, the fine arts. So 99% of the time you don't need an expensive photo editing program. Unless you enjoy giving money to Adobe.
Photoshop may have more fancy filters, but using a filter is the fastest way to advertise you're inexperienced and a hack. 99% of the time prefab filters a bad idea. The best work is nuanced color and composition.
As far as brushwork with a stylus, I wouldn't go there. I have a bachelors degree in Drawing and I owned a Wacom for years, and let me tell you, it's a silly substitute for the real thing, with any program, on any computer, at any resolution. If you really want to be an artist, break out the charcoal, oil paint, pencils, and scan your work. A machine will never simulate the viscosity of water, oil, it's not about math, it's a different universe.
I don't really think it is that weak a comparison. Because as I mentioned I could do everything I require (creating simple graphics, bgs, icons etc) without Photoshop using GIMP. This may not be the case for everyone but they are definitely worthy of comparison in my opinion. Basically GIMP is free and can do everything I need, so why would I pay any money when the results are just the same.
Doesn't other commercial digital image editing software does the same thing? like Color Correction, Basic Graphic design, and has tools like cropping, resizing and others...
For instance Commercial Software X (e.g. PhotoPerfect, Coral PaintShop) has everything Gimp Has more or less.
So, instead of comparing the Commercial Software X with Gimp, we compare Gimp with Photoshop, where photosop is way ahead of any image editing software I know.
Basically my point is, when we compare stuff, we should compare anything that has similar service. (e.g. Bluehost vs Hostgator, Dreamweaver vs Expression Web) But Photoshop vs Gimp is tad bit weak.
I've never heard of those other programs, PhotoPerfect?
Chronologically, first there was Deluxe Paint, http://en.wikipedia.org/wiki/Deluxe_Paint which started out on Amigas (PCs couldn't do graphics yet and Amiga was really popular with artists) and this spread to PCs with DPII once VGA became more popular. Maybe Apple had something back then but it wasn't mainstream.
Corel briefly had something popular for business use, if you needed to make pie charts, bar charts, that sort of thing.
For the most part, nobody had enough memory to do photo manipulation until around 1990 when you could buy a somewhat affordable 386 machine that was fast enough, and remember, scanners cost $1000 back then. This is when the era of the pixel-editor ended and Photoshop rose to power, and nobody has challenged Photoshop since then.
OK, there are good vector-based programs out there too, but GIMP/Photoshop are not in that category.
All these other little freebie graphics programs that come with hardware you buy (printers, scanners, cameras) maybe they do basic functions, but why bother learning these "bonus" programs if you have access to Photoshop or GIMP?
GIMP is obviously a copy of Photoshop. It's very, very similar to Photoshop, if you can't see that, then maybe Photoshop has changed too much since earlier versions, which is maybe another reason to keep using GIMP, fewer changes for the sake of change.
It was an easy transition for me, from Photoshop to GIMP, even though running Linux applications on Windows was not very easy at first, you can't beat free. GIMP would be even more popular if there weren't so many illegal "warez" copies of Photoshop out there. So this is a good reason to learn GIMP, it's free, you're not breaking the law using it, and it works just like Photoshop.
Why not compare MS Windows and Linux Ubuntu, or Wordpress and FrontPage, or any other commercial v's open source software?
The fact is that GIMP, like many other OS products, provides people with a free way to do stuff that they would normally have to pay for. Yes, it cannot do everything as efficiently and smoothly as the latest Photoshop, but it can do a lot, and for most people it does everything that is required. If you need more, you buy more. The sad thing is that a lot of people still do not even realise that there is so much open source available.
In fact, a better analogy would be to compare MS Office with OpenOffice.