The U.S. government has made 66.5 million economic stimulus payments worth almost $57 billion. For those still waiting, hang on. That mind-boggling number represents only about half of the total set to go out by mid-summer.

Just getting a check may not stop the questions. More than a few taxpayers have been disappointed by their windfall. Or, as the Internal Revenue Service puts it: "I received my stimulus payment but it was less than what my friends and neighbors received. Why?"

David D. Stewart, IRS media relations specialist for the state of Pennsylvania, said the question has been coming up with some frequency. "There is some confusion out there, I guess, because people aren't aware there are particulars that may affect the dollar amount they get."

The truth is not everyone is going to get the full $600 amount ($1,200 for married couples) and $300 per child under 17. "There are nuances and rules and exceptions," he said.

A single person whose income tax liability was less than $600, for example, may get less, as would a married filer whose liability was less than $1,200.

On the other end, single filers with adjusted gross income above $75,000 or married ones with adjusted gross income above $150,000 may see less than the maximum.

Those who owe back taxes or have federal debts such as student loans or child support obligations also may see smaller checks.

There are quirky situations, too.

Not long ago, the IRS found a glitch that meant the government didn't notice the dependent children on about 350,000 returns.

Those parents should receive separate checks starting sometime next month. The agency estimated less than 1 percent of the 36 million returns eligible for such payments were affected.

Anyone who used a tax preparation service and directed the government to pay that service out of a tax refund can expect to wait for a paper economic stimulus check, rather than look for a speedier direct deposit.

Comparing notes with the neighbors or the folks at the hair salon might not be the most accurate way to determine how much money is coming.

Officials such as Mr. Stewart keep trying to herd everyone toward the Web site -- www.irs.gov -- where they keep adding answers to new questions and where people can use an online calculator and their tax return to figure out their personal situation.

Told that some people have complained it's hard to get through on the government's rebate hotline -- 866-234-2942 -- Mr. Stewart said he had not heard of problems. But he urged those who don't have Internet access at home to find a nearby library with Web services and those who don't have online experience to recruit family members who do.

The Carnegie Library of Pittsburgh doesn't know if people have been using its computers or wireless connections to get rebate information because it doesn't track the sites people are going to, said Suzanne Thinnes, communications manager.

But she said anyone who wants to do so is welcome. "If they don't have a library card, we can give them a guest pass."