Is there no end to airlines' creativity in extracting money from us for services that once were free?

Apparently not, judging from the latest option that United Airlines announced this week: Pay a $249 yearly subscription fee and you (plus up to eight people traveling with you on the same reservation) get to check up to two bags per person, per flight for free all year.

In fact, the so-called Premier Baggage program may be worth it, if you don't mind handing United all that money up front. But you'll need to do a little math to see if it might work for you. And you'll need to join Mileage Plus, the airline's frequent-flier program, too.

Typically, certain high-mileage frequent fliers (and up to eight people traveling with them), plus passengers in first class and business class, already are exempt from fees for first and second bags. So this program doesn't help them. And United already lets coach passengers check two bags for free on some international flights, depending on the destination.

As for other customers:

Potentially, families and groups who travel together and frequent fliers who don't already qualify for fee exemptions benefit from this.

For instance, by buying the Premier Baggage option, a family of four could get their money back or more, by flying one or two round trips per year, depending on how many bags they checked. A single traveler would need to fly three to seven round trips to offset the subscription fee, depending on the number of bags checked.

United's first-bag fees are $40 each per round trip on domestic flights, or $160 total for four people. Combined fees for first and second bags are $100 per person per round trip, or $400 total for four people. (These figures are based on paying the fees at the airport; if you check in and pay for your bags online, you save $5 or so per bag each way.)

Infrequent fliers, light packers and inattentive online users don't benefit. Inattentive online users don't because the fine print on the offer says that at the end of your subscription year, United automatically will charge your credit card for another year's subscription ``unless you have opted out of the auto-renewal feature.''