When is there ever good news about credit cards? It’s true that they've driven many people deep into debt. But at the same time, over many years (albeit not lately), they've provided some good earnings for investors in companies that issue cards, such as Capital One (NYSE: COF), JPMorgan Chase (NYSE: JPM), and Citigroup (NYSE: C).

The credit card arena is changing these days, though. There's a reason why the trouble we're going through on Wall Street is being called the credit squeeze: It suggests, correctly, that there will be an impact on credit card users. Their credit will get squeezed, too, along with that of big corporations!

We've already started to see some of the effects on credit cards. As Bill Hardekopf, CEO of LowCards.com, has noted, there are two key likely developments for credit card users. First, lenders will be stingier with credit (and this is reportedly already happening). To get the best interest rates on their cards, consumers will need excellent credit scores. (Lenders are suddenly a little more concerned with taking on riskier borrowers.) Credit limits will also be lowered now and then.

What does this mean for investors -- in banks that issue cards or in the card companies themselves? A lot depends on their credit exposure. Companies like Visa (NYSE: V) and MasterCard (NYSE: MA) don't bear any credit risk, but if transaction volumes fall, their profits could suffer. Meanwhile, those that do extend credit directly, such as Discover Financial Services (NYSE: DFS) and American Express (NYSE: AXP), can expect to see dollars a little harder to come by. They may end up doing less business, but at least it'll be of a higher quality, with less money lent to riskier borrowers.

There's likely to be a ripple effect, too, affecting retailers, for example. Many consumers may rein in their spending in a shaky economy. At the same time, others may not, and as they approach their credit limits and their rates get hiked, they'll end up in credit death spirals. So as you look at investments in the coming months and even years, keep this perspective in mind.