What is a social strategy I can use to respond to "How's your PhD going?" I was surprised when starting my PhD as to how much I get asked this question and how much I fail at answering it. Whenever I attempt an answer, I fumble around and the subject immediately changes after. If I state exactly how it's going, the stress of publishing and intensity of the program comes off overly negative. If I state what I'm working on, I either lose them or bore them. 

What's a good social strategy to respond to this question?
"It's going well, last week I made some good progress on X. How're things with you?"

The vast majority of people are just asking to be polite. If they're actually curious for specifics, they'll follow up with a more specific question. I personally like to have some kind of a cute story about my research because nobody has any idea what pure math people actually do. (I draw fractals for a living, so I have some pictures on my phone to show around.)

EDIT: Some of the comments bring up relevant points about cultural differences. If the local culture is one in which asking out of politeness is frowned upon (ie German @O. R. Mapper, or grad students @JiK), I think it would be still best to start an answer of the above form. This allows people to either gracefully exit or pursue a more in depth description according to their own interest and cultural mores.