The thing about a gun in this discussion (since most people are fairly civil in this thread) is that the OP was asking if a gun was a good tool to have in a household. The important word there is tool (someone else mentioned this earlier too).
If the household requires the gun as a tool then it is valid to say the gun is a good tool to have. This may be applicable in circumstances such as farms or somesuch where the gun is required as a tool. This would mean that when not used it would be suitable to keep the gun locked and secure away from anybody who wishes to reach it for the purpose other then for which it is kept for. The gun serves its purpose(s) in the household and that is all.
Questions concerning the gun for self-defence in the household are a different matter. Claiming the gun as a tool for other specific purposes and then attempting to justify it's ease of availability under circumstances of duress is not acceptible as that means you are intentionally keeping it for the additional purpose of a possible break-in. Under these circumstances the gun would easily serve to escalate the situation as assumptions concerning the intruder's armanment and ability would largely be invalid unless one assumes an intruder of high danger in weapons and ability. If one were to think any less of the intruder then the homeowner could make a gravely inadvisable decision.
Even with the expectation of a heavily armed and trained intruder what good would a gun do? If you got the jump on the person then you would be heavily injuring them (at the least) with minimal knowledge of their intents, identity or possible threat. This places you in a position of wrongdoing if you are attacking such a person. If you get to a face-off or similar situation is it worth it to threaten to use a gun or use it when there is the very real danger that someone will die or be injured, and if it is you then the rest of your family may be in increased risk. Is that worth it for your possessitions? Pulling out a gun places you in greater danger ethically, physcially, and in the eyes of the law.
Australia has had very strict gun controls since the Port Arthur Massacre; which resulted in more deaths then any other rampage of that style in the USA, UK or any other country of similar circumstances. This has resulted in responsible gun ownership among those who do legally own their guns, as they have to follow stringent regulations. As a consequence it is much more difficult for others to procure and own guns without a permit.
The last time I remember hearing of legally owned gun-related crime was concerning an armoured-truck guard who overstepped her responsibilities while on the job and as such was repremanded accordingly. I can only remember one circumstance of illegally-owned gun crime in the media since the restrictions were brought into place and that involved gang conflict, not intruders to homes.
Generally, an Australian person will be capable of describing to you the benefits of having an (almost totally, especially in urban areas) gun-free society. The presence of a gun may be helpful in certain circumstances, but this must be weighed against the innumerable circumstances where more ill may occur then good. Hence the gun is not a useful tool for a household.
