Customers wait their turn to order, pay and possibly tip at Diesel in Davis Square. (Photo: Alistair Croll)

Cambridge Day is part of a project called Voices of MainStreet — a weekly, nationwide Q&A in which editors at the money and lifestyle site MainStreet.com ask questions and bloggers answer them. For this entry, I was asked about the dark side of being frugal.

I’m part of the problem in the workplace coffee shop, which for me means Diesel in Davis Square. Despite being a regular coffee shop with desserts, awkward Craigslist dates and pool tables, the place can all too often and easily look like study hall before finals (because it probably is). If the laptop is the most obvious indicator of seriousness, Diesel frequently hosts enough of them open on tables to suggest things have progressed beyond problematic into the apocalyptic.

I’ve plugged in at Diesel for entire days, walking there when I wake up and writing until they kick me out, and that means using their electricity as well as possibly removing from use one of the coveted cushioned booths — which I might feel worse about if their rarity and my occupancy weren’t actually tearing down social barriers. (Sure, it’s apples and oranges, but anyone concerned about a loss of civic engagement in the face of ceaseless computer use should check out how people meet and interact at Diesel. It’s a sociology major’s thesis waiting to happen.)

It was worse when I was unemployed, since I needed the workspace more than ever but certainly couldn’t afford an $8.25 sandwich, especially accompanied by a $3 drink. Sometimes I instead bought a bag of Diesel’s day-old bagels and ate those; sometimes I furtively ate granola bars from my backpack. Sometimes I literally ran down the street for cheaper food — a slice of pizza or Anna’s quesadilla. Guilt.

Worst of all was that in addition to taking up space and sucking up electricity, I wasn’t tipping. Every Thai iced tea was simultaneously delicious and shame inducing; every time I got 10 stamps on my card and a dollar off was a twist of the knife; and reusing a glass and saving another dime was the final insult.

The baristas, of course, probably knew none of this and cared not at all, but for me working at Diesel this way was like living through a particularly esoteric short story by Poe, like I had to keep myself from shrieking in remorse at the checkout, “I admit the deed! Here, here! It is the gleaming of that hideous tip jar!”

This isn’t just academic — get it? — or white, middle-class liberal guilt. I feel alarm because along with anthropological dissections of workplace coffee shops, The New York Times has covered the movement away from them and toward a more European model of coffee bar. (The model says you gulp your espresso and get the hell out.) And it’s disconcerting that one of the prime examples of the model is just up the street a ways in Arlington, at the well-regarded Barismo. The last thing I want is for Diesel to lose money because it’s inadvertently become a incubator for money-losing businesses run by the sneaky unemployed.

But I’m no longer unemployed, and I don’t have to be sneaky. Don’t get me wrong: I still can spend whole days there, taking up half a booth while distressed mothers circle helplessly with sobbing toddlers and uneaten brownies, but that usually means two meals bought there and at least two drinks, with a dollar dropped in the tip jar each time. Surely I’m still part of the problem, though, which makes me wonder if Diesel’s a better case study for economics than anthropology.

Maybe that’s what all these people are working on around me?

Postscript: It’s worth pointing out that in addition to the things I mention above, which can seem like negatives, as a result of my Diesel abuse I am also in the shop buying stuff at slow times; introduce people to the place and otherwise give it good publicity, including by writing about it; meet people at the place frequently, adding their buying power to my own; and even buying Diesel merchandise. I’m hoping it all balances out. (Added Aug. 2, 2011.)