Though reluctant to mention Groupon and LevelUp in the same sentence, Priebatsch points out that the daily-deals company often makes more off of a merchant in one day than credit card companies make in a year.

FORBES: Interchange Fees Are For Suckers: LevelUp Hints At The Future Of Mobile Payments

But while people buying an old one-day pink travel card could use it on the buses, Tube and overland rail, many train companies refuse to accept the equivalent pay-as-you-go on Oyster.

BBC: An 'oyster' travel card, sitting on top of a card reader

Caution: holding a Green Card for even one day during a year taints the entire year.

FORBES: High Cost To Go Green: Giving Up A Green Card

Bolten officially was sworn in Friday to replace Andrew Card, who had been chief of staff since Day One of the administration.

CNN: New Bush aide tells staff to expect more changes

But a few months ago, Murphy was a day late paying one of her bills, so she called the credit card company to try to get the late fee removed.

NPR: Some Consumers See Credit Cards Canceled

One day my son asked a series of questions about how money gets on the credit card.

FORBES: Forget Cash - Teach Kids About Credit as Early as 6 or 7 Years Old

One-third of American adults plan on sending an e-card this Valentine's Day, according to a recent study by the mobile testing company SOASTA. Digital cards are most popular with men between 35 and 44, and spouses were the most common recipients.

CNN: Bacon chocolate, e-cards and other Valentine trends

You need to set up a corporate structure, hire a book keeper, separate the business money from your personal expenses (corporate bank account, business credit card etc.) You should be on top of the financials from day one.

FORBES: David Bach on How to Build a Career Without Going Broke