I've done, and helped a bunch of people do them.

I have the 80percentarms jig that was linked, and it works very well. It's gotten to the point that when I crank one out for one of my builds, I spend about 1:15 on it and I have a lower ready to go. I have another one that is 95% drilling to finish, and then a quick finish pass with an end mill. It came with my 9mm 80% lowers so I figured I would give it a shot.

Considering that I am spending $39/lower, and have already paid off my jig and tooling, the price is pretty nice, but I am also a fan of no paperwork.

I thoroughly enjoy the 80% stuff because it's more of a project than just bolting stuff together. I've got 80% 2011's, 1911's, P228's, AR-15's, AR-9's, AR-10's, 10/22's, etc... My wife just shakes her head and chuckles when UPS and Fedex show up...