I think most posters here are missing the point. Yeah, sure, the OP should sign up for the program -- it costs nothing (besides the time that it takes to sign up to monitor one's account).

The more relevant question is whether he should exhibit any loyalty behavior -- principally, concentrating flying on one airline or steering all possible other loyalty-point-earning scenarios to his frequent flier account.

And the answer is, not necessarily. If you fly 5,000 miles per year, then that's 25,000 miles in five years, or enough to get a free flight on most programs. So, you could join a program and get a free flight every five years, which is not a trivial award (if the flight that you want is available for an award redemption -- which is a big if).

But if you are like most travelers, and choose each flight based on price, convenience, or other factors, then you might not fly the same airline or alliance every time, and the benefits of forcing yourself to do so -- the free flight every five years -- might not be worth the cost.

It's also an exaggeration to assume that one can get miles doing things that one already does. Most of the big-earning possibilities are via credit card, and there are plenty of other credit card rewards -- e.g., cash back or merchandise rewards -- that are more valuable to many people than frequent-flier miles. Even other loyalty programs like hotels' provide reward options other than miles that might be more valuable to some travelers.

Of course this is FlyerTalk, and most of us (including myself) place perhaps an irrational valuation on frequent flier miles, but that doesn't mean that they are for everyone.