Okay, as promised, here is my finanical philosophy of FF point value: 1 point is worth 2 cents.
I come up with this not based on some airline insider information, but just on judging what I would use the points for. You can always find deals on the airlines to travel places. Salt Lake to Atlanta for $179 roundtrip, Anywhere to Vegas for like $99, etc... It really doesn't make sense to use your hard earned travel on such a cheap flight, unless you have no other choice. For me, I would not use FF miles to fly a domestic trip unless the trip was going to cost me $500 or more. Hence a $500 ticket costing 25,000 points means that a point is worth 2 cents. If you want to be conservative, use 1 cent, but either way... those points are still worth something.
Miles vs Segments
Another caveat to be aware of is the segments clause.
Whereas before I have stated that it takes a certain number of miles to earn elite status in a frequent flyer program, you can also earn the same status by flying many (shorter) flights. In fact, that is how I earned Platinum Medallion on Delta. The Delta chart is something like this:
When I was living in NY and working in Detroit for a year I would come home almost every weekend. I flew Delta which offerred only connecting service through Cinncinnati. I was young and not in much of a hurry, so I didn't mind the connection. This meant that for each round trip, although I would only earn a small amount of actual flight miles, I would earn 4 segments (LGA-CVG-DTW-CVG-LGA). It only took 25 times of doing this to get 100 segments. So even if you are only travelling a short distance, the segments can really add up and help you. Again, the point is don't stray from your primary airline.
Partnerships
If you are travelling, but are absolutely unable to get a flight on your preferred primary airline (the one you have built up the most base miles with that year) then check to see if the airline has any partners. Star Alliance (which includes United domestically and many other airlines internationally) is what you would hope for from a partnership. With little exception, all benefits and segments, and points and bonuses are fully transferrable from one airline to another. For example, if you wanted to fly United, but had to fly Air Canada instead don't worry about it. Just give Air Canada your United number and you will earn everything as you would had it been a United flight. But beware, not all partnerships are what they appear to be. For example, Delta and United will allow you to accrue miles on eachother, but you don't get the segments and it doesn't count toward your base mileage on either airline. In my opinion this scenario is just not worth it. Better to earn the miles on the airline that you are flying in that case, unless you are absolutely positively sure that you will never fly them again.
International flights are no fun in coach, but with the tips from this site you should be making your way to business class soon. The thing to be aware of is that international segments count for more than domestic segments. Where above I said that you needed 100 segments to earn Platinum Medallion on Delta you can actually do the same with 20 international segmenets. In otherwords, internation segments are 5 times better than domestic. Or, another way of looking at it, you are 5 times dummer if you miss getting miles on a international segment compared to a domestic segment. "Get miles for every single flight you take"
If you do end up making it into business class on an international flight you are in for a treat. International Business Class is a far better place than Domestic First Class. The seats are bigger, they recline farther, they have footrests and builtin TVs with many movies to choose from. The only thing even remotely bad about international business class is that it is not quite as good as international first class. For International First, imagine a suite at the Ritz Carlton, on an airplane. On United, International First seats sit individually (nobody next to you!) and have more room than a small New York apartment. Delta removed all of their international First seats and now only have "BusinessElite" (read: business). But unless you are a CEO or independantly wealthy, most of us can just hope for company paid business class tickets, with the occassional dream of upgrading to first.
Children usually fly at 50% to 75% of an adult fare. Sometimes there are deep discount fares that are not reduced for children, but some discount is usually available. If your child is under two years old and you don't mind holding them on your lap then you don't need to buy them a ticket. If you have two adults, and one 1 year old travelling with you, and you get creative with your seat selection then you could pick the two outer seats of a three seat block for the two adults, hoping that the middle seat will not be taken (they are the last to fill up) and you may get lucky and get a seat for your child for free.
We recommend Expedia for all online purchases. Although all the major airlines offer online purchasing, and some even offer 1000 bonus miles for purchasing there, it is nicer to keep everything in one place. Fares are the same no matter where you go (Travelocity, Expedia, Yahoo, etc...) - but sometimes there are slightly cheaper fares on the airlines own page - not for the majority of flights, just for the flights that their computer projects will not be full over the next few days.
Profiles
One of the greatest thing about expedia is what it remembers. You can store everything, from FF numbers, rental car info, passport info, drivers license numbers, and your preferred credit cards (we recommend the United Mileage card) all right there. And the best part is, you don't need to go to one special screen to enter the information. The first time you book a ticket there it will remember it for you. When you go back, you will be pleasantly surprised to see that it remembers you want your aisle seat with the low salt meal and it remembers your FF numbers better than you do. For my family, with 4+ people usually travelling, this really comes in handy.