I loved the size, weight, and screen of the MacBook instantly, but put off getting one after reading all the flak about it not being usable for "real work". Heck, I've even heard sales people at the Apple Store say it. But eventually, my love of ultra-portability and retina-displays won, and I got one anyway (to replace my rooted, Arch-running, ex-Chromebook.) And I love it. Sure, I don't expect as much out of it as my 13" Pro (work machine), and I spend most of my time in the shell and vim rather than post-processing video or 3D rendering, but this thing is a joy to use.
It's not for everyone (or every computing task), but if you have a preference for the smaller screens and portability, and are aware that you're willing to trade raw machine grunt for this portability, then I wouldn't write off the MacBook just because "someone on the internet" said it wasn't usable.
I've got an XPS 13 which has a similar form factor to the 12" MB (304mm x 200mm vs 281mm x 197mm) and love it as well for all my tasks. The key is the screen - pack in a reasonable number of pixels and it's perfectly usable.
I picked up a larger macbook pro last year. One thing I find myself doing often is loading images from a sd card from my digital dslr camera. The usb type c is still not my cup of tea.
I honestly haven't tried working with large image files as I don't normally do that so I don't know how the processor would handle this. The problem I had with the rMBP... ...is that I was not taking it often with me.
It's not for everyone (or every computing task), but if you have a preference for the smaller screens and portability, and are aware that you're willing to trade raw machine grunt for this portability, then I wouldn't write off the MacBook just because "someone on the internet" said it wasn't usable.