on 3v3, starting 2v1 may work but watch out strike back, 2 of 3 are defenseless, forces being away, it's not easy for the remaining guy to defend 2 allies against 2 enemies.
starting 3v1 not only denotes a serious lack of sportive spirit , it's also quite stupid, this guy rushed out, everyone is defenseless.
Other nice tactics when successful:
the nydus rush
the zerg tower rush
the hunt of every overlord with, let say, corsairs, pawning in air (cool against people who let their overlord packed at same spot)
the tank drop near the minerals or the gas, in preference in altitude
dark templar rush against a terran can work quite well also (as terran turret come quite late)
damn I miss those great moments...
田畕畾畕田 - Mage Herborist/Miner/Grinder