I had it done a few years ago when I cracked a tooth, the crack went down below the jaw bone so they had to do the crown lengthening to expose a little more of the tooth before they put the crown on. As far as the procedure itself went, I thought it wasn't nearly as bad as a root canal. The periodontist was wonderful, worked very efficiently and the whole thing took about 45 minutes. No discomfort at all, they had me really, really numb. I also appreciated that they topped off the novocain right before I left so I'd be able to pick up the Vicodin and get home before it wore off.
I spent the rest of the day on the sofa stoned on Vicodin and with an ice pack on my face, napping on and off. It ached, but it wasn't unbearable. The pain was gone by the next day.