Due to renovation work, Qantas will be banning members from taking guests into its Perth Qantas Club Lounge between January 18 and the end of May. Even if you don't live in Perth, it's a useful reminder that taking guests into a lounge isn't an automatic privilege.
Under normal circumstances, Qantas Club members can bring one guest with them into a lounge when travelling, and the same applies to annual members of Virgin Blue's The Lounge. However, both airlines (and other international operators) reserve the right to refuse to admit guests if the lounge is overly full. Having that happen is rare, but certainly not unprecedented, so bear it in mind the next time you're travelling with family and friends.