I have booted a PC, unintentionally after she called me saying she was goiong to leave the group. Being concerned, and wanting to be a good friend I asked why, and if there was anything I could do. Should we as a group discuss her concerns as adults? This is when things went down hill. Everything was everybody elses fault. Nobody treated her with the respect her years of gaming experience required. I played favorites. This person was a min-maxed twink. Etc. At this point I realised maybe it was the best for her to go if she felt this strongly about eveybody in the group, including my wife, her biggest suporter in the group, always acting condescending torwards her.
Things built from there and it ended in a great big fight amongst the whole group. I shut down the campaign, and restarted a new one with only the players I felt I could game with. I'm still not sure what caused her to go off on everybody, but, I have to say she had a real over inflated view of her own gaming skill after listening to her. IMO. She had no problems with the rolepalying, no clue how to run any of the mechanics. Which was normally fine, we could help, but this I think was one of her sore spots.
On the other hand I've been removed from a group as well.

The DM had an issue with me, and I'll admit I was not having fun, and this was most likely evident. The vibe I got from the DM was that he really didn't want me there and he could not seem to get beyond his issues with me no matter what I tried. He and I had been frineds since high school, close ones I had thought. So when he asked me to leave I did so without an issue and an apology. It was when he told me that everbody in the group had a problem though that I really took pause. These were my friends, and I didn't want them to think of me as a jerk.
I called each of them to offer my apologies, and to tell them I had no hard feelings, and no problem gaming or hanging with them any time. This is when I found out none of them had any issues with me, and that they had no clue what the DM was up to until after they got there that night to game, and I wasn't there. They each told me they would game with me any time. I took them up on it and formed a new group and gamed on a differnt night. This became the core of my first group that I DMed for over two years.
So a word of advice. If you're going to remove somebody from the group, make sure you do so honestly. I still would have bowed out, even if it was only the DM having an issue. But he felt the need to make it the whole groups decision instead of his alone. By putting words in his friends mouths, he ended up losing a few of them, and they still have yet to forgive him several years later.
-Ashrum