I did the trek. I don't know the exact weight of the harness and vest but I would say it was less than 10 lbs definitely. My guess would be it was only around 5 lbs total and that included my camera that got attached to the best and the water bottle they gave us that was attached to the vest.
I didn't feel like I was adding alot of weight when they put it on me.
When DH and I tried to go in Fall 2011 the weight limit was 310 without the harness. They weighed him without the harness and he was 311, so we couldn't go. It was my impression that as long as he was 310 without the harness that he would have been allowed to go. He tried removing things from his pockets to no avail. The CMs were really nice about it though and we were able to get a full refund. That was two years ago though, so they may have adjusted the weight limit slightly.