I am not by any stretch of the imagination an introvert. Such a trait would have been a major liability growing up in the military where either you or the folks around you were picking up and moving on to the next assignment almost as soon as you'd settled. Now, I'm not entirely sure I'm an extrovert, either. I just learned how to adapt to my constantly changing surroundings. Mostly.
That being said, I never considered running errands or shopping to be a way to socialize (unless you bring the friends along with you and you shop together). Now, if we're standing in a line or oohing and aahing over the same product, sure, I might strike up a conversation if the mood seems right or the person seems amenable. I've had nice chats with folks around playgrounds, too, while we watch our kids cut loose. (I've also had intensely awkward conversations around playgrounds too, but that was because the need for a deeper connection was so palpable for both me and the person I was talking with that we couldn't easily do the superficial thing; it's hard to be polite and talk about the weather when the subtext screams "I need a friend! Please, be my friend!")
So I had some mixed reactions while reading JA Konrath's post about handselling your own books to folks in bookstores. On the one hand, he lays out excellent advice and gives plausible scenarios that are very informative to folks who need some help on how to handsell. On the other hand, I kept wincing. When I go to a bookstore, it's almost always because I have a specific goal in mind: find this book, or browse the SF section for something fun. I'm in my own world, looking at all the shiny shiny. If I want assistance or an opinion, I'll ask for it. The couple of times that another customer has actually talked to me in the stacks (maybe after seeing me trying to decide between two books or something), I haven't enjoyed it. It feels like an intrusion, another shattering of the illusion of being surrounded by stories just waiting for me to read them. As a customer, I would not like being approached by an another trying to handsell a book. Hell, I wouldn't enjoy being approached by a bookseller trying to handsell a book. If I want a handsell, I'll find you.
I can't see myself approaching customers who aren't in any way signalling receptability in a bookstore during downtime at a signing. If a customer's looking around as if lost, I'll talk to them and see about bringing the conversation around to my books if what the customer is looking for matches up. If a customer approaches me, of course I'll go into extrovert mode. If a customer is hemming and hawing over books that match up with mine, I would have to weigh the situation carefully to make sure an approach wouldn't annoy. If it's really slow, I might also put a note on the table with my books that says "Hey, I'm wandering through the SF stacks, looking for items to add to my TBR pile. Come find me and give me recommendations." Or something.
Of course, that's all very hypothetical since I have not a single published title outside of my master's thesis, and only two copies of that are on shelves and only at the University of Colorado library. I'm sure they'll go flying off that shelf as soon as I make it big, because what rabid fan wouldn't want to read about how I attempted to purify an enzyme and analyze the kinetics of its reaction?
As an interesting aside, I should note that I'm likely to be much more comfortable at a signing in a Borders store as opposed to a B&N store. Most of that stems from having met with my critique group in a Borders weekly for four years. But the rest of it is just because B&N gives me a very formal feel. I have a hard time relaxing and browsing as a customer in their stores because I always feel like if I touch anything, I'm going to set off alarms. I think it's the dark wood and dark green decor. Borders has brighter woods and colors. There's also quite a few open walkways whereas the B&N stores I've been in crowd their walkways with displays, making me feel claustrophobic as well (a perception not enhanced by having higher stacks as well; you can't look over the stacks in a B&N to see the whole store the way you can in a Borders).