(MONEY Magazine) – You're no doubt familiar with frequent-flier plans. YNow get ready for a new twist: frequent-buyer programs that reward you with everything from free travel to -- get this -- annuities if you buy specified products or services from companies affiliated with the plans. Trouble is, the deals may not deliver much real value to you unless you are remarkably devoted to the participating companies' products. Two new frequent-buyer plans -- Air Miles and Start -- were unveiled in publicity blitzes this spring. More are expected later this year. Air Miles has signed up some 200,000 members; Start, 27,000. Are they good deals? You be the judge. If you sign up for the no-membership-fee Air Miles plan (800-547-2212), you earn mileage credits when you patronize any of its 13 member companies, including Hertz, AT&T, Frito-Lay and Time Inc. (publisher of Money). Example: If you rent a Hertz car for a weekend, you get 25 mileage credits. Once you amass 500 miles, you can begin cashing in your credits for air travel on Air Canada, American, United and USAir. Problem No. 1 is that unless you purchase big-ticket items offering lots of mileage credit, you've got to buy a whole lot of everything to get much of anything. To pile up the 500 miles required for a New York City to Boston round-trip ticket, for example, you would need to buy, say, 1,000 gallon-size bottles ($1.19) of Clorox bleach. Which brings us to problem No. 2. Even if you bought all that bleach, Air Miles wouldn't give you credit (at one mile for every two bottles) for more than the first eight bottles you bought in any single year. In other words, to get that ticket, you'd have to buy the 1,000 bottles of bleach over the next 125 years; all we can advise is, start young. The program places similar restrictions on most of its other packaged goods. Finally, problem No. 3 is getting credit for purchases. For many items, you must go to the trouble of cutting out proof-of-purchase labels or collecting vouchers and mailing them to Air Miles. ''The concept isn't to get a free trip by just buying popcorn,'' says Air Miles spokesman Michael Miles. ''You do it by combining a number of products like staying at a Hyatt hotel and making AT& T calls.'' The Start plan (800-955-7010), which demands a one-time $25 membership fee, bills itself as a painless way to save for retirement. Its advertising says that a couple in their thirties could build up $178,000 by age 65 simply by patronizing Start's 11 sponsors, including Club Med, MCI, Eddie Bauer and Spiegel. To do that, however, they'd have to spend more than $7,000 a year on the plan's products. Basically, Start is a jazzed-up cashback program. A percentage of the amount you spend with participating companies -- 1% of the first $1,000 a year, up to 6% on total outlays over $2,000 -- is placed in a non-interest-bearing bank account. Once the account reaches $100, you can invest it in a Metropolitan Life fixed annuity, currently paying 6.25%, or you can simply withdraw the money quarterly. Some financial pros dismiss Start out of hand. ''The idea that you can spend with abandon today and save enough for retirement is patently false,'' says Ann Terranova, a financial planner in San Francisco. Counters Start's founder ; Lawrence Andreini: ''We never say join Start and don't save anywhere else. Most people don't save. We want to get them to begin.'' Bottom line: Consider Air Miles if you purchase its companies' products regularly and don't mind clipping labels until your fingers ache. As for Start, if your true goal is to amass retirement savings, cut your spending and consider investing that money instead in the investments in this month's cover story, ''Where to Put $1,000,'' on page 70.