I've only done it twice. The first time was unplanned and we had no tent or sleeping bags. We stayed in the hut and slept on our climbing ropes. It was miserable, mostly due to the lack of a sleeping pad and limited water to drink. It wasn't terribly cold.
The other time was closer to Trail Crest and it was in the middle of winter. It was a very warm night, in the low 20s. Nobody else was camping there but plenty of people marched past.
I think camping on the summit and near Trail Crest happens a lot these days. As long as you're prepared for the temperature and altitude and are willing to haul your water up and your poop down it's no big deal.
