I used to have PS. I got really proficient at it and knew all of the keyboard shortcuts like the back of my hand. I could fly around the program as easily as I could skip down the road. Now, I am on a linux machine and thus can't install PS. So I have installed GIMP. I have been able to find ways to do pretty much everything I could do in PS in GIMP (or at least that I have tried yet) but have had a distinct learning curve getting used to the shortcuts and tiny differences in the interface.

My suggestion to you, unless there is something specific in the opposite program of the one you are using (PS in your case), there is no need to switch. For the most part, unless you are doing work professionally, there should be no need ever to switch that I know of. Both programs are really good programs.