Mixing ground and neutral

[Tim Lindstrom]

Hello BP.  I pulled the front panel off the breaker box to inspect the work my contractor did when he re-wired my entire house.  I was surprised to see that he mixed neutral wires and ground wires on the same bar in the panel.  And he put 3 wires in each hole and screwed them down.  I have heard that you should put no more than 2 wires in each hole to prevent arching.  I have heard both sides to the neutral/ground mixing.  Some say as long as the bars are bonded, it is ok, others say it could still cause a shock hazard.

Any electricians out there that can help me out?