I have a J&S jack and do not think twice about it being on the jack, and I never tie it down. If I was pulling forks or something like that, I would tie it down, but for normal things like washing, changing oil, etc, it's always fine. I leave it raised on the jack, with the safety catches engaged, all the time when the bike is parked in the basement. Not fully raised, but with the tires off the ground about 6". I can roll the jack with the bike on it all over the basement if I need to move it or reposition it for servicing. The J&S is very stable. I have the oil pan adapter as well...works like a charm. I've done everything from change the entire exhaust system out, to changing both wheels at the same time, without ever using tie downs. Here's a link to see the jack and watch the video:
http://www.jsjacks.com/products/motorcycle-lifts