NEW YORK (TheStreet) -- Americans have been recruited to do a host of jobs that we aren't getting paid a cent for: Shadow work.

Much of this new form of pseudo-employment, explains Craig Lambert, involves all those little jobs that companies once had to pay employees to do, but that they now foist off on their customers: pumping our gas, scanning and bagging our groceries, depositing our own checks and such.

"Many many things are in the self-serve economy," says Lambert, author of the new book Shadow Work: The Unpaid, Unseen Jobs That Fill Your Day, "and from a business point of view, it makes perfect sense, for an owner to have their customers do the work for nothing, instead of paying salaries to a staff person to do it."

He places our commutes in that shadow work category, too: They amount to time we are donating to a business. While Lambert isn't necessarily suggesting that our employers should pay us for commuting -- which, he notes, takes up an average of about 200 hours a year, the equivalent of five work weeks -- he does suggest that many of us start discussing with our bosses whether there might be better alternatives for both parties.

Also propelling the shadow work economy forward are interns. "You could look at interns as a competitor to salaried employees," he says. When unpaid, they work for the privilege of the job, doing tasks that would otherwise require employers to hire staff. And even when they are paid, their low wages drive down the bargaining power of experienced, full-time workers. Meanwhile, in the wake of years of corporate downsizing, more tasks have been piled upon the smaller numbers of individuals who remain, without additional pay.

Because we're still near the beginning of the shadow work era, we can't say with any specificity how this trend is affecting the unemployment rate: So far, nobody has done the research. "But clearly," says Lambert, "jobs where there is essentially, a very low skill level, ... those jobs will be very vulnerable."