Ed Yozwick, Post-Gazette Graphic: Online tracking You must have Adobe Acrobat Reader to view these files.

Last week, customer service agents at FedEx Ground received an unusual complaint: A man's package had arrived a day early.

The package had been shipped on a Monday from San Jose, Calif., for Friday delivery. Using FedEx.com's online tracking function, the man saw that by Wednesday afternoon, the package was already at the Pittsburgh sorting facility on Neville Island, just miles from his house.

So, even though he'd paid for five-day delivery, he couldn't understand why FedEx didn't get him the package two days early.

"It's unusual to get a complaint from someone whose package arrived a day early," said FedEx Ground spokesman Rob Boulware, chuckling at the thought. "But they see it [online], and they want it."

As hundreds of millions of Americans buy presents in the upcoming weeks, tens of millions of them will track their packages on the Internet.

But while online tracking has been an unqualified success since its inception a little more than a decade ago, it's also had some unforeseen side effects. The more information customers know, it turns out, the more entitled they feel to demand customized services. Knowledge, as they say, is power.

"The expectations of the customer are higher now than they were 10 years ago," said Howard Schmid, senior manager of FedEx Ground customer service centers in Pittsburgh and Cincinnati. "The more information you provide, you're giving them more to go on."

All major shipping entities, including the U.S. Postal Service, now have some version of an online feature that allows customers to enter a tracking number and find out whether their "Little Mermaid" DVD has made it from New York to New Stanton.

At UPS alone, online tracking has grown from 100,000 users a month in December 1995 when the service was launched to an expected 25 million users this year on the company's peak shipping day of Dec. 20.

And at Moon-based FedEx Ground, customer service agents have grown accustomed to handling calls they wouldn't have dreamed of a decade ago.

On a daily basis, said Mr. Schmid, the company gets calls from customers who see online that their package has reached a local sorting facility and want to know if they can pick it up themselves, rather than waiting for the truck to come the next day.

"We will try to make those accommodations," he said, adding that occasionally, if the situation seems particularly urgent, FedEx also will try to speed up package delivery midstream.

Providing "behind the scenes" information to customers is something that companies find themselves doing partly to lower costs or drive business, and partly to keep up with their competitors, said Baohong Sun, a marketing professor specializing in information management at Carnegie Mellon University's Tepper School of Business.

"Whether it's good or bad, it's going to change customer behavior," she said. "They invite the customer to share in the process."

The vast majority of shipping customers, of course, are able to share in the process without making outlandish requests.

Mykal Duffy, 33, of Delmont, is an avid package tracker who admits the occasional bout of frustration along the lines of "It left Plum seven hours ago. Why isn't it at my door?"

But it's never gotten to the point where he has actually called to complain. "There's never been a time where it's been so unreasonable," he said. "Now if it was in Plum and in transit for three days, I would definitely call."

Mr. Duffy, a manager at the Carnegie Library of Pittsburgh, shops online every couple of weeks and takes great pleasure in tracking his packages. When he simultaneously ordered his iPod and accompanying radio tuner, for example, he amused himself by envisioning a race between the two products to get to his door first.

And to his great surprise, the iPod (shipped by air from Shanghai) beat the tuner (shipped by truck from Harrisburg). "I probably would have lost money on that one," he said.

For ardent shoppers, online tracking serves to fill the anticipation gap between the time the purchase is made and when it is in their hands.

"I guess I probably don't need to do it," said Denise Beasley, of Stanton Heights, who buys about 80 percent of her purchases online and always tracks them. "It's just more interesting if you do it."

For businesses, however, tracking programs can help with practical matters of when to schedule employees to process shipments, or how much storage space to clear. Both UPS and FedEx offer special business-oriented tracking programs to monitor both outgoing and incoming packages.

"The retailer can see everything coming into their address," said Steve Holmes, a UPS spokesman in Atlanta. "Otherwise, you wouldn't have a way to do that. You wouldn't know you had 200 returns coming in on Wednesday and 500 on Thursday."

Other special features include e-mail alerts when a package has encountered a delivery problem and FedEx's digital transmission of the signature of the person who received the package.

The shipping companies have been able to use online package tracking as a marketing tool, but they also believe that it has saved them money in dealing with customers.

UPS has calculated it saves money by avoiding "where's my order" calls, which cost between $2.50 and $3.50 when call center salaries and infrastructure operations are figured in.

The same goes for shipping company clients, many of whom incorporate tracking information directly on their own Web sites. "Tracking is important to a retailer, particularly at this time of year," said Mr. Holmes. "If they can cut telephone calls out of their call centers, they're saving real dollars."

But how much tracking information is too much?

At FedEx, the company scans packages as many as 25 times, said Roman Hlutkowsky, vice president for operations technology and system support. About nine or 10 of those scans go up on the Web site for the customer to see. The rest, which might indicate that the package has emerged from different internal sorting groups, wouldn't make sense to the consumer.

"We walk a fine line," he said. "Although we might have a lot of information available, a lot of it isn't meaningful."

In terms of adding additional information, Mr. Hlutkowsky also has to keep perspective on the bottom line. The most hard-core package trackers, for example, would love to follow their individual purchases through global positioning systems -- an option that Mr. Hlutkowsky describes as unlikely.

"When we deploy technology, we don't want to do it just for technology's sake," he said. "There's got to be some payback."