What are your experiences with getting a seat that you want vs one the airline wants to give you.
What airlines are most prone to give you the seat you want?
Do you get it at boarding only - if so, what airline?
What are some tips you can offer so travelers can get the seats they want?

The best way to get the seat you want is to KEEP TRYING. Request the seat you want when you are making reservations, then again when you are confirming reservations, then again when you check in, and if you still haven't succeeded, try again at the gate. Several years ago, I was flying on American and was on crutches (can you believe they tried to gate check them??!!! what was I supposed to do, sit in my seat and WAIT for someone to bring them to me??) and really needed a bulkhead seat. Persistence finally got the seat for me, but only when I asked for the third time at the gate.

Also, if you are a fan of emergency exit row seats, the best time to snag those is exactly one hour before scheduled departure; and it seems you are more likely to get them if check in at the main terminal (rather than the gate). Also, when traveling as a couple, willingness to be separated by the aisle makes your chances of getting emergency exit row seats better.

The best way to get the seats you want is to be a platinum-level frequent flyer -- no one else's needs are considered if you make a request. Second best way is to be an airline employee with seniority, dead-heading on a flight with plenty of friends. Third best way is to be a male, dressed to the nines, arrive early, be polite but insistant. Fourth best way is to be very lucky with your reservation agent -- I call back when I hear a voice that sounds clueless or imperious and try again until I get someone who sounds like they completed high school in less than 5 years and who seems not to hate people.

Hate to break it to you but the senior airline employee who is dead-heading is usually given the "dreaded center seat" in the back of the airplane that doesn't recline because its in front of the lav. Trust me!

If you tell them when you make the reservation that you will be in a cast, or recovering from surgery etc. and will have a letter from your doctor, they will even bump people from bulkhead seats for you. American, for one, has a special person who deals with special needs. Yes, they will try to take your crutches because they are a danger if they fall on another passenger. But, they should be willing to get them for you at any point in the flight so you can use the rest room for instance. And, on our last flight on UA the last middle seat went to a flight crew member in uniform who was deadheading back home. Unfortunately as one more passenger showed up he was bumped up to the center jump seat over the console in the cockpit which is probably the least comfortable place imaginable. I do agree with the calling back if you get a totally disinterested person on the phone. That is, if you don't mind waiting another 10 minutes!

Most airlines save the better seats, exit rows, bulkhead and forward row aisles for thier elite FF travlers. I am a platinum on Delta and pretty much get what I want regardless of when I make a reservation. Interestingly, thier midwest partner, Comair has a policy of not pre-assigining exit rows to anyone, even elite FF members. I have protested this every way I can think of to no avail. Other Delta Commuters (Skywest and ASA) will preassign exit rows to Elite FF travlers.

On the rare occassion that I have to travel United I find that if I go to the airport the day before travel I can get assigned an exit row seat (I am not an elite Milage Plus member). Fortunately, this is a small town and the airport is convenient.

Alaska and NW, forget about it.

Just to clarify the point re: the crutches -- I wasn't trying to hang on to them or place them in my row; they fit in the overhead (perhaps they were taking up valuable space for those oversized suitcases?). And no amount of begging over the phone would convince them I should have a bulkhead seat. I guess they needed to see my pathetic little self, hobbling around, in person before they would have any pity on me.

Which leads to the next point: most airlines want to see for themselves that you are able-bodied before they will give you the exit row, which is why they won't otherwise pre-assign it. Frankly, I think its a good policy.

The "crutches" tip is total nonsense. I'm a disabled traveler who requires a wheelchair. I am not accomodated, more like "tolerated".