Half of those with rewards credit cards plan to redeem cash or points this summer to enhance their vacations, according to May’s edition of the Capital One Rewards Barometer. This is a quarterly tracking study that measures credit cardholders’ attitudes to many sorts of rewards programs, not just those run by Capital One itself.

Rewards credit cards at vacation time

Drilling down into the study’s data reveals just how holders of rewards credit cards plan to use their vacation redemptions. The top-three categories were:

1. Airfares: 58 percent of respondents
2. Hotels: 42 percent
3. Gas: 18 percent

The study’s data also show the enduring popularity of these rewards programs. More than 90 percent of respondents, all of whom have rewards cards, said that they were satisfied, very satisfied or completely satisfied with theirs.

Problems to avoid

In spite of all that satisfaction, some consumers encounter nasty surprises when they come to redeem travel-related rewards. In a press release, Amy Leander, vice president of rewards programs at Capital One, observed:

Flexible rewards programs that allow cardholders to redeem their rewards when and how they want can make that vacation dream an affordable reality. When choosing a new rewards program, consumers should consider both the value of rewards and the ease of using them.

You shouldn’t assume that flexibility is automatically built into your travel rewards program. Particularly with flights, but sometimes also with hotels, you may encounter blackout dates that make booking impossible for popular periods of travel. And some plastic — even some airline credit cards — don’t allow you to redeem points to pay for fuel surcharges, taxes and booking fees. So that “free” flight could end up costing you a significant cash sum.

The trick here? Make sure you understand the terms, conditions, limitations and exclusions that apply to earning and redeeming cash, points and miles before you sign up for rewards credit cards. And that applies to hotel credit cards; gas cards and simple cash-back plastic as well as airline-branded ones.

Foreign transaction fees another factor

Another way in which vacationers sometimes find themselves stung by their plastic is over foreign transaction fees. Many credit card companies charge these, although some issuers (including Capital One) don’t.

Of course, this doesn’t bother most of us most of the time. But these fees are often charged at a rate of 3 percent, so, if you’re planning a once-in-a-lifetime trip abroad, you could easily find yourself hundreds of dollars better off with a credit card that doesn’t charge them.

Rewards credit cards worthwhile

Don’t be put off applying for rewards credit cards by these revelations. There’s a reason over 90 percent of those who have them are pleased they do. But it is worth investing a little time exploring this site’s credit card lists to make sure the plastic you end up with is actually going to deliver the benefits you need and expect.

Published 05/22/12 (Modified 09/12/12)