It's quite easy, if you have a decent set of instructions, take the trouble to equip yourself with the right files and abrasives, and if you go slowly and test-fit frequently. I did it once, with a made-to-order Dlask custom-length Gold Cup trigger, and I wouldn't hesitate to do it again. Only took a couple of hours.
I think I'd gotten the basic instructions off a very old post on the pistolsmith.com site, and on an old e-mail from John Lawson (which I printed out and still have, somewhere), but the various American 1911 fora must have this kind of thing stickied to death.
Note that I'm not talking about trigger jobs, though; for hammer/sear engagement adjustment and trigger-pull lightening, I'd send everything off to a competent pistolsmith. But installing the trigger itself is 95% stock reduction and polishing. A kitchen table job.