GIMPs great. Before I even picked up a camera I used photoshop, paint shop pro and some other editors. Never liked any of them. I became a Linux user too and thought it was great that Linux distros give you GIMP and windows users have to make do with MS Paint out of the box. Anyway I didn't like GIMP either. I don't think any photo editing software is easy or intuitive all of them need to be learned. Anyone who says they just opened PS and knew how to use it straight away is telling pork pies
I use windows and linux every day. If my windows computer breaks, i can usually figure it out in a few hours, if my linux computer breaks I can usually fix it in minute. Considering 5 years ago all i used was windows thats progress 
Anyway, I decided I needed to learn one of the photo editing software options. I shoot manual mode and nothing else, most of the time my flashes are manual too and I like to get it right in camera first time. But occasionally you do need to give the levels or curves a tiny kick, or do your black and white conversions with a bit more control.
When you run both side by side its striking how the results for most edits is identical, the process to get their is almost always identical. I can look at a photoshop tutorial and almost always do it 95% the same in GIMP. What is striking is the cost factor. GIMP free, learning GIMP is mostly free due to the great communities out there. PS costs a bucketload, and if you want to learn it you will find no end of people looking to take your money for a book/dvd/course. For what I do with photo edits PS offers me nothing more for that huge premium.
Now don't get me wrong if I find one day GIMP is holding me back I'll replace it, but that has not happened in years, and the development pace of GIMP is way faster than PS at the moment so whatever gaps do exist are shrinking significantly almost every 6 months.
When it comes to raw however, DPP can work for most things, i just don't like the interface and it slows me down. UFRaw at the moment doesn't suit me as its really a single image solution, but its only on version 0.17 or something so I'm keeping an eye on it. So I have invested in Capture One for my Raws. Capture does such a great job that I hardly ever have to open GIMP, usually I do just to see if I can make any kind of useful edit, but more often than not the Capture output is perfect.
Leaving cost aside I have a free copy of Photoshop Elements through my work. I have it installed alongside GIMP. In the last 2 years, I've never once used Elements. I've opened it a couple of times but straight away felt like closing it again. GIMP is right for me and I have had to deal with other peoples PSD files, not been an issue and I can give them back a PSD file they can open in photoshop too.
I've noticed that some people do have a "security blanket" relationship with PS/Elements. They feel they need to have it to be accepted and safe. I think its a bit of an issue in photography at the moment when everyone aspires to the same camera, same lenses, same software and same processing technique. Sometimes you have to mix it up a little....
FYI I'm an amateur who is very secure in using
Canon Digital Cameras(is it 2010 already)
Canon and Halinna Film cameras(still cool)
Sigma and old MF lenses (for their rendering style)
Capture One (for my rendering style)
and GIMP (for icing on the cake stuff)
I rarely need to PP



