I've been using PS for a good couple years and have used gimp in the past. Although being good for a freeprogram, gimp just isn't as powerful as PS like mentioned. I recently made a tut for a head I made in PS but made sure gimp users could do it too and everything had to be dumbed down so much for gimp to handle it.
It's like having a race between a F1car and the Flintstones-mobile but Fred's has square wheels on.
It's worth taking on the short learning curve, you'l find it's better. Although I actually prefer CS3, CS4 eats more pc juice and the 3d side is abit to be desired lol.
But the main reason to switch to PS would be the brush settings, gimp is in the same boat as mspaint in comparison to PhotoShop's Brush customization in my opinion.