I see this is a good place to launch into a pet rant...

My pet rant: the airlines have established FF programs in a legal netherworld that allows them to manipulate the programs relatively at will and provides little consumer rights/protections. There are government regulations that extensively cover tradable commodities, currencies, coupons, rebates, lotteries, discount programs, sweepstakes, gift certificates, etc., etc., etc. But FF miles are not legally considered any of these things - and there is little accompanying regulation about how the programs are run.

Personally, I've benefitted from the programs greatly. I have - for the most part - gotten awards when I've wanted them. I have milked many promotions for maximum advantage to score "free" vacations for very low cost. I'm glad that the ludicrous notion that the IRS could value FF miles as a currency never went anyway.

But still, the thought that the airline effectively sell miles to you as part of their primary product, and then provide no consumer rights associated with them, is unsettling.

Coming back on-topic: joining the FF program doesn't reveal much additional information to the airline that they can't already get. If I chose not to join (which would be silly, because I have to "buy" the miles associated with the flights either way), they could still match up my name, address, credit card, etc. and find out where I'm going and for how long. These days, the only way to conceal that information is to use something like Greyhound. (At least I think you can still ride the Dog with cash and no ID.)

I participate actively in the programs, so they know I hold credit cards. They know I eat at restaurants. They know I order flowers. If I was freaked out by all of this, I guess I'd move to Montana and live in a log cabin miles from nowhere. But since I travel frequently and use credit cards all the time, I just assume that The Man is watching regardless of whether I join the programs. You gotta buy the miles with every segment you take: might as well accept them even though they are flawed.