I'm a programmer that tinkers with side projects where occasionally I'll create a very basic logo or do some image editing. I don't want to spend a lot of money on an application I'll only open once a month or so. I'm on a Macbook Pro.
I've always used GIMP, so it wasn't an issue for me but for those coming from Photoshop there is a version of GIMP that supposedly works more like PS (more similar buttons, functions, etc.) called GIMPshop.
I just found an open-source one called Krita that looks promising (works for Mac, Win & Linux) -- no crappy GIMP interface. For paid Mac Photoshop alternatives, I think Affininity has a better interface than Pixelmator.
NOTE: For simple edits, Pinta is an exact clone of Windows' Paint.NET.