When people choose to study or work at a café as a substitute for an office or a library -- sometimes spending four to six hours at a time sitting in the coffee shop -- café owners hope that they will adhere to the unwritten rules of conduct.

These rules, however, are gray. How long is it appropriate to sit in a café without buying something? If you pop for a sandwich and a drink, should you be able to spend as much time as you'd like working in the café, or should a customer purchase more items if planning to stay in the café for an extended period of time?

Sometimes, the "rules" are blatantly ignored or abused, but for the most part, café customers play fairly.

"When people started 'officing' all day long in cafes, it was more of an issue. Now, people are more accustomed to working mobile," says Dave Blanchard, the director of stores for Alterra Coffee Roasters.

Blanchard says the mobile working culture more or less regulates itself, and most people recognize when there are more customers than there are tables. Hence, many café dwellers choose to buy something to stay in their seat guilt-free.

"Most people are aware that if they're going to hang out all day and not buy something, they're going to feel guilty," says Blanchard.

Most of the Alterra cafes have unlimited Wi-Fi usage, but some -- like the popular lakefront and Prospect locations -- have an "on / off" system that limits customers to a certain amount of free wireless time during peak hours.

"(Prospect and Alterra at the Lake) are so rockin' that we have to limit the number of campers hanging out all day," says Blanchard. "But we leave it wide open until the noon hour, when things get really busy."

Blanchard says the decision to include only two outlets in the plans for the new Alterra on Humboldt café was not a ploy to discourage customers from hanging out for too long.

"This is an absolute coincidence," he says.

Alterra co-owner Lincoln Fowler says more outlets will be available at the Alterra on Humbodt in the future.

"The whole facility needs attention to complete now, and the outlets are part of a long and growing list," says Fowler.

Steve Hawthorne, the executive manager of sales and marketing for Stone Creek Coffee, says people should pay attention to the environment, and relinquish their seats as needed.

"We never want to push people out the door, but sometimes we do have space issues. After two hours or so of sitting in the cafe, and drinking only one cup of coffee, it would be polite to give your seat to new customers if they are walking around, looking for a table.

"But if the cafe's empty, then of course we encourage customers to stay as long as they like," says Hawthorne.

Evan Michael Scott runs a small business and spends a portion of his work week in Milwaukee cafes, researching on his laptop and making phone calls. He believes the rules should be more straightforward.

"These are public places, and if the owners want the public to obey rules, they should state these rules, post a sign or something," he says. "If I spend $10 or more on a sandwich and a coffee, I should be able to stay as long as I want to."

Sheila Pufahl-Bettin, who owns Brewed (formerly Anodyne Coffee Company), 1208 E. Brady St., says she encourages customers to buy another item if they want to stay more than a couple of hours at her café.

Brewed customers are entitled to a free WEBbeams card, allowing them two hours of free service. After the two hours, customers can purchase more time via WEBbeams. In some cases, particularly if they purchase more food or drink items, they can receive another free two-hour card.

Pufahl-Bettin recognizes these rules get sticky -- that they're hard to implement -- and that sometimes it's difficult for staff to keep track. Luckily, she says, most of the time her customers are respectful.

"Most people are fair about this," says Pufahl-Bettin, who purchased the business last October with her sister, Eva Kuether. "A purchase of anything after two hours is a great thing. We just don't want people to take advantage of the situation."