Tips for choosing and using frequent flyer programs

This weekend, I'm taking a $450 flight for free.  As you probably guessed, I'm using frequent flyer miles to do it.  This is actually the first time I've redeemed miles, because most flights I take cost $150-$200 roundtrip, and it seems inefficient to use an award good for any domestic flight on a ticket that cheap.  So I was patient, and lo and behold, this situation came up where I needed a $450 ticket, and out came the miles.  This is an important (though obvious) tip for using frequent flyer programs-- get the most out of the rewards that you can.

Also, on this trip I'm traveling with my boyfriend, who rarely flies and isn't interested in accumulating miles.  So I actually put the award into his name, and the paid ticket is technically for me.  This is because paid tickets earn you miles and award tickets don't.  When redeeming awards, give the paid seat to the person who most needs/wants the miles and the free seat to the person who doesn't.

Here are some other things that I've learned about frequent flyer programs.  (I should let you know that I fly with intermediate frequency, about 10-15 times a year; if you fly constantly for work, or if you rarely fly, your experiences may be a little different, although I've tried to make this as broadly applicable as possible.)  I'd love to hear suggestions and tips from other people as well.

Without further ado:

• Sign up for the frequent flyer program for every airline you fly.  They're free, and it never hurts to get credit for your flight, even if you're pretty sure you're not going to fly that airline again, because you never know what'll end up happening.  (If you don't get a chance to sign up before the flight, you can usually sign up afterwards and get them to retroactively credit you.)  However, and this is not contradictory...
• Focus your flying on one or two airlines.  Try to concentrate your flying, and therefore your miles-earning, as much as possible.  This is hard if much of your travel is for work, but you may be able to specify priority airlines, or if you're lucky like me, you can pick your own flights as long as the price is the cheapest or comparable.  If you're paying out of pocket, obviously you don't want to pay a lot more just to fly on your primary airline, but if the prices are the same or comparable, you can focus in on your target airline(s).  To make this easier, you should...
• Pick airlines that have your city as a hub, or travel heavily out of your city.  It's also useful to keep an eye on the airlines that fly to the cities you travel to most often and/or have a hub there.  In many cases, you can find one or two airlines that will consistently have the lowest fare on most flights you want to take, which makes compiling miles much easier.
• Figure out if you want a program based on miles or segments.  If you tend to fly long distances, you probably want your flights to be counted by miles.  If you fly a lot of short hops, you may be better off with a program based on flight segments.  
• Look out for programs' expiration policies.  Sometimes you have to use your credit within a certain amount of time; in other programs, as long as you keep your account active by earning miles, they'll keep accumulating indefinitely.  If you're not going to earn enough credits to use before they expire, the program won't do you much good.
• Hunt around for special bonuses.  For example, if you're a college student, you can join the College Plus program at United Mileage Plus and then get 10,000 miles just for graduating college!  (That's 40% of what you need for a domestic ticket.)  I'm guessing there are similar programs on other airlines.  Do you know of any good bonus deals?
  
• Consider credit card options carefully.  There are a lot of ways you can go about combining your credit cards with a frequent flyer program.  In my experience, most of the ones that have no annual fee don't earn you enough miles to make it worth choosing over a cash-back card.  A better deal might be one of the annual fee cards that give you a big mileage bonus for signing up (especially if you have a flight coming up you want to use miles for and the bonus will put you over the top).  These cards will typically waive the fee for the first year, and you can either cancel it after a year or keep it and pay the fee. Obviously you'll want to consider the implications for your credit; some people sign up for and then cancel these cards over and over again, but I don't recommend it.  The annual fee cards typically give you a better miles to dollars payoff than no-fee cards, and if you charge a lot on your credit card, they may be worthwhile anyway; the math has just never worked out that way for me.
  
• Look for non-flight ways to earn miles.  Most airlines have "partners" that'll let you earn miles by eating out, staying in hotels, renting cars, buying groceries, and much more.  For me personally this makes up a very small share of my mileage earning, but for someone who doesn't fly much and/or spends a lot of money already with an airline's partner(s), it could be very helpful. 
  
• Look for non-flight ways to redeem miles.  As with any rewards program, things that cost the least miles/points are probably the worst value, but if you're not going to end up with enough for a flight, you might as well get a free magazine. 
  
• Donate your miles to charity.  If you have miles sitting around and it seems hopeless that you'll ever accumulate enough to redeem them for anything, many airlines have programs where you can donate them to charities (to help fund travel for humanitarian aid workers, sick kids and their families through Make-A-Wish, etc).
  

What are your tips, suggestions, experiences?  Please share...

P.S. A great resource on frequent flyer programs is FlyerTalk.