I would recommend what xylord said especially regarding explosives. I would also recommend disabling energy collectors and energy condensers, as they allow players to enter creative mode lite within a day or two of joining a server, which would wreck any attempt at an economy for a server. Mass Fabricators can also be used to spawn matter, but it can't make everything, and requires a lot of EU to make anything, so its somewhat balanced. There is also a discussion on BC, mainly pipes, causing lag here: http://forums.technicpack.net/threads/how-much-lag-does-buildcraft-actually-cause.17691/.