I haven't done it myself, but a semi-handy coworker did (I believe Ikea ones) and this was the only home project that defeated him. You apparently get to learn how out of square your walls really are and all sorts of shimming techniques in order to do it right. I'm sure there's some practical ways you could design your cabinets that mitigates these challenges - I think corners are where things really went awry.
We did the cabinets to go on our last remodel. I had to go out of town for a few days for work and when I got back the Wife had assembled most of them.. if that tells you anything.
I did Cabinets To Go when we redid our kitchen around a decade ago. If you have a basic nail gun and moderate competency using it then assembly of them is pretty easy peasy. Once I got an idea of the scope of the project through the guy at the CtG store showed me how he had a contractor who would come assemble/hang/mount them for $40 a cabinet and I was quickly sold on signing over that work.
