DS is still going at 2.5, though he's a lot less interested since I got pg. I still feed him in public - until I got pg, he would always feed without fail for 5-10 mins at every toddler group, swimming lesson, church service, visit to friends etc. I don't get any comments. :)
I got more comments (mostly people asking when I was going to stop) when he was 12-18 months - after that, I think people either assume you've stopped or they decide you're just odd and leave you alone about it. Actually, lots of people don't even notice, even when I bf with them around 
If anyone did ask, I'd say 'it's good for his health, good for my health, prevents / calms tantrums, soothes pain and gets him to sleep. I can't see any reason there why I'd want to stop'. The other one I've used a lot is, "I'll stop when one of the three of us (DH, DS or me) wants to stop," which is suitably vague and can't really be argued with. 
I don't think either my parents or my PiL approve. PiL have stopped ever mentioning it (ie it's now on the List of Taboo Subjects). My parents have asked occasionally when I'm going to stop. Each time I tell them one good reason why continuing is a good thing (eg helps his eczema) or use my standard lines above. They don't argue, as it's always a new piece of info for them.
No-one in the family has even mentioned it since I got pg, which has surprised me (I'm 18 weeks now). Again, I suspect I've just been confined to the 'odd' category.
Bf has really helped DS's behaviour, and his ability to sleep. When I first got pg and he had less milk, and at other times like when his facial eczema hurt so that bf was uncomfortable, there were so many more tantrums and sleepless nights.
I'm hoping he'll carry on feeding, as it's too useful a parenting tool for me to want to lose.
The book EauRouge recommends is great, both on continuing to bf and on weaning.
And I agree you might be surprised by people's reactions. I felt a bit twitchy about feeding DS at a church we were visiting on holiday recently (especially since DH was trying to 'network' with a view to future employment opportunities). The woman behind said to me afterwards, "So are you planning to tandem feed once the baby arrives?" and it turned out that she was tandemming, as was another mother there. 