I was wondering the same thing. I have a feeling that the cost of electricity isn't the entire concern.
The hanging out all day and not buying anything in addition to plugging in the computer would make most shop owners become a bit frazzled. When the culprit is a creepy guy who makes the staff and customers uncomfortable ... then that's a bigger issue.
One of the problems is that no one has found the optimal way to integrate wi-fi into the coffeehouse setting. You have to agree that the wired cafe is "a different animal." It looks and sounds different from a traditional cafe, and it feels different. People also forget that free wi-fi means free wireless access to the Internet, which doesn't include using an electrical outlet.
I've seen several coffee shops that require a person to buy at least $5 worth of food or drinks before you're allowed to plug your laptop into their electical outlets. For some people, that would seem reasonably fair. Another strategy would be to require a minimum purchase for every hour spent in the store, which would be difficult to keep track of.
However, it appears that the best solution is to either cover the electrical outlets, so people can't plug in their computers, or post a sign saying that people can't plug in. It sounds like the sign idea (discussed previously) is working.
At some point you'll need to deal with wi-fi campers (they're also called laptop campers or table campers). The problem is how to deal with them so you don't lose their business or lose other customers because of them.
How about offering two hours of free wireless access per day and then after that, having it cost $3.99 for a two-hour session? Has anyone tried something like that?
The people who come to most coffee shops represent a wide range of socioeconomic strata. Some are students living off of loans. Some are professionals. Some are homeless. Some are middle class American tourists visiting from out of town. Some are parents. And some are seniors living off of fixed incomes. As a result, there is a great diversity in what the patrons are reasonably able to pay for your services.
You want your cafe to be a warm, inviting, and inspirational space where people could come to get their work done, hang out with friends, and drink great coffee. Putting restrictions on what people can do while they are there would undermine that mission. You want them to feel welcome and comfortable, but the problem is where (and how) do your draw the line?
Rose