DP and I are not ttc, we are waiting to ttc #1, due to financial reasons. As we are both getting on a bit (I'm 30) and not married yet, we tend to get small talk along the lines of 'when are you two going to get married and start having babies??' I wouldn't dream of asking anyone, even my immediate family, about their family planning issues, so it's hard for me to know how to answer a question like that.
My honest answer to this is - we are going to wait until we have gotten out of debt and can afford a bigger flat. DP and I have discussed the sensible option of waiting for about a year and are both happy with it. However we have had some strange reactions:
- Some friends are a bit better off than us and one in particular can't seem to get their heads around how we could be in this trouble in the first place. It ends up with us being lectured on how to budget, by someone assuming we must be spending frivolously, and I get upset. If I wanted a conversation like that I would give Edwina Currie a call!
- Some friends have families that are supported, either partly or fully, by welfare (and I personally don't think there's anything wrong with that), who have taken my statement of 'we are going to wait until we can afford to have kids', as a personal attack on their lifestyle.
I have actually entertained the idea of telling people we can't have kids, just to stop them badgering us about it. It winds me up that people who have problems conceiving are, quite rightly, given sympathy, but God forbid anyone should choose to wait a bit!! Do they realise I'm not doing so just to spite them! 
I feel like I can't discuss this without someone finding something to get offended about. I would love to just say, 'That's a very personal question.' and change the subject, as I would if it were a stranger asking. But I accept that some people are nosy and like to stay in touch with what is happening in their loved ones' lives, and we don't want to upset anyone by excluding them. What would you say?