I suppose it depends on what you consider a "pro" or not, and what you are using Photoshop for to begin with.

I started out 20 years ago as a retoucher and digital pre-press. 20 years later, I'm back in the publishing game, but publishing on the tablet. The magazine I am producing as the "eat your own dog food" test run of our bootstrapped tablet publishing tools (see https://www.youtube.com/watch?v=22qqsFHH1HY or https://www.youtube.com/watch?v=YXlHFhbqzHU for more info) is almost entirely photography and video. Guess who is doing the "pre-press" work? Yeah, that's me.

So let me run you through my typical retouching workflow I use to retouch a fashion photo (discussion about perpetrating negative stereo types of female body types ignored for the sake of this conversation):

    - Open the image in Photoshop
    - Duplicate the background to a new layer and convert to smart object
    - Open up the smart object into a new document
    - Liquify, patch tool, liquify, patch tool
    - Hair, pimple removal with clone stamp
    - Masked adjustment layers for very slight color correction, typically make up and teeth and eye whitening
    - Save smart object
    - Go back to original document
    - Duplicate smart object twice
    - Highpass filter + overlay blend mode on top most smart object copy
    - Smart blur on smart object copy beneath high pass
    - Mask the blurred smart object and start painting in skin smoothing on the channel mask
    - Now at this point, I might have gone back to the smart object and made some more clean up and liquify tweaks
    - Manual corrections done, I move onto color grading and color correction

All of this is done with a wacom tablet, which afaik, GIMP still has issues with (usable but not on the same level as photoshop). Liquify tool in gimp is a horrible joke. No smart objects.

Can you do this process with GIMP? You can. I have. It's not as easy or straight forward as it should be though. It can't be stressed how important Smart Objects are to the modern photoshop workflow.

So as someone who uses Photoshop not only for app design, but actual honest to goodness professional retouching, I have to say if this guy is only using Photoshop 10% of the time, he's probably not even the target market for it. Will GIMP ever make it to actual competion for Photoshop on the professional level? I sure hope so, but not anytime soon. Photoshop CC (I've been using Photoshop since 2.5 on a Mac Quadra 950) is the best version ever. I know I sound like an Adobe shill, but I have extensive expertise that goes back decades now.

Now you damn kids get off my lawn.