Thank you Fly-by-Wife.
And in particular, in relation to :
How many people blithely continuing to use XP would have any clue whatsoever that their PC may be being used for such a purpose? Having malware active on a PC is not necessarily apparent to the user. Believe me, the cleverest malware isn't.
Indeed. Some of the most modern malware out there doesn't even install itself in a traditional manner, all you need to do is point your web browser at the wrong website and boom, someone has a nice little backdoor activated on your machine running in RAM at kernel level. Virtually undetectable and you'll never know, because you never downloaded anything and never clicked "ok" to any dialogue boxes, it just happened quietly in the background. Doesn't have to be a dodgy website either, could be a good website that just got hacked.
And no that isn't some sort of sci-fi dream, there are already live exploits out there that Microsoft have patched for this sort of thing on 7 and 8, but left untouched on XP.
As time goes on, they will only become more prevalent and more sophisticated.
So I repeat, XP has no place on the internet. And since most people can't live without the internet these days, XP has no place in your home.
You wouldn't live on a dodgy council estate and leave your front door open and the keys in your car. So why do the same in your computing life ?