Ti riporto due esperienze recenti:
I-VALE... in questi casi si dice... ci sei o ci fai?

un conto è parlare delle esperienze personali che sono appunto soggettive e dipendono da mille variabili, un conto è parlare della policy che ciascuna compagnia adotta.
Ti riporto un sunto delle regole dei carrier americani sul same day change fee.
Personalmente lo trovo interessante perché in molti casi permette di posticipare (oltre che di anticipare) un volo a cifre ragionevoli e soprattutto pagando la fee si ha il posto confermato anziché stare in stand by (che per poche rimane ancora rimane gratuito).
In ogni caso le regole diverranno sicuramente più stringenti visto che queste fee sono state introdotte da relativamente poco tempo e il pubblico deve ancora "digerirle".
Una volta che sarà considerato normale pagare la same day change fee, è possibile prevedere che spariranno le opzioni gratuite di standby per le poche che ancora lo fanno...
Airtran Fee: $25.
American Fee: $50
Passengers can call Reservations or handle the transaction at the airport ticket counter or Self-Service Check-In machines. If eligible seats are available within 12 hours of departure of alternate flights for your same itinerary, your flight change can be confirmed. Also, American continues to offer the same-day option of standing by for an earlier or later domestic flight for eligible fares at no charge. See rules.
Continental
Fee: $50 ($25 for OnePass Platinum and Gold Elite members)
The same-day flight change option will be available within 24 hours before your original scheduled flight. Inside of this timeframe, you can try to take an alternate flight so long as it departs no more than 12 hours from when you are making the request.
You may take advantage of this same-day change option when traveling on Continental Airlines, ExpressJet Airlines, Inc. dba Continental Express and/or Continental Micronesia. Changes may be confirmed within three hours of your new desired flight at any airport check-in kiosk or with an airport agent. You may also contact Continental Reservations by phone.” See rules.
Delta
Fee: $50
“The same-day confirmed option allows you to change your flight time on the same day of travel for a fee of $50. To use the same-day confirmed option, you must confirm your new flight within 3 hours of the scheduled departure time. If you have a flexible fare (usually a refundable ticket), you may be able to change your itinerary without a fee.
A $75 fee applies to restricted Delta Shuttle fares when changing to a peak flight time.
You can use the same-day confirmed option for travel within the United States, Canada, Puerto Rico, and the U.S. Virgin Islands on Delta and Delta Connection® flights.
No changes between origin, destination, or co-terminals (such as New York’s LaGuardia and JFK airports).” See rules.
JetBlue
Fee: $0-40
"Same Day Flight Change
Cities with Multiple Flights a Day
* You can make your confirmed same day changes via 1-800-JETBLUE or at the airport beginning at midnight (in the time zone of the departing flight) of the same calendar day as your original scheduled flight.
* You must travel on an earlier or later flight the same-day.
* You must travel between the same city pairs.
* A Same-Day Change Fee of $40 per person will be applied for your confirmed seat.
Cities with One Flight a Day
The same-day change program is not available for cities with one flight a day.
Standby Travel
In order to travel standby, you must have already purchased a seat on JetBlue.
Cities with Multiple Flights a Day
* You must contact JetBlue within 24 hours of your original flight.
* You are allowed to travel on the flight prior to your original flight only, regardless of whether it is a non-stop or connecting flight.
* You must travel between the same city pairs (specifically, the origin and final destination BlueCity).
* This option is free of charge.
* If you are booked on the first flight of the day you cannot fly standby on the last flight the day before. However, you may jet standby one flight after your scheduled flight."
Northwest
Fee: $50
Northwest allows WorldPerks / SkyMiles Platinum and Gold Elite customers to standby for earlier flights and will not incur a fee if space becomes available.
“Northwest Airlines today expanded its popular FlyNow option, which permits confirmed flight changes within three hours of scheduled travel for a $50 fee, to now include flights throughout the entire day of departure. Previously, customers wishing to confirm day of departure changes for flights departing outside of the three hour window were assessed a $100 change fee.” See rules.
Southwest
Fee: None, but you may end up paying more than on any other airline
This airline is a whole different animal. While most customers love the fact that if you change your travel dates on a non-refundable fare and decide to travel within a year from the original flight (even on a different route), you’ll be able to do so without a fee, it’s a whole other situation if you want to fly same day on a different flight. Although they don’t state this anywhere on their site (that we can see anyway), if you’re on, say, a $99 one-way fare leaving at 5 PM and you want to leave now on the 2 PM flight, while there’s no “fee” as such, you will have to pay the difference between your $99 fare and whatever the current “walk up” (no advance purchase) fare is on that route, which could be hundreds more. As with other airlines, Southwest sometimes looks the other way, but if the gate agent isn’t in a generous mood that day, prepare to pay.
United
Fee: $75
“You can confirm a seat on an alternate flight on the same day of travel anywhere United flies within the United States and within four hours of the time of your request. If eligible seats are available on an alternate flight, your change will be confirmed and you will be charged a $50.00 fee.
To request a same-day travel change, check-in at an EasyCheck-in kiosk at the airport or at EasyCheck-in Online. You may also contact a customer service representative at the airport check-in counter or call 1-800-United-1 (1-800-864-8331). See rules.
US Airways
Fee: $50 (waived for elite frequent flyers)
“We allow you to 'move up' to any earlier flight on the same day of your originally scheduled departure time at the airport (with the exception of flights to Hawaii and Europe). You can only make day-of-departure changes at the airport (and not by calling Reservations).
If there is an open seat available on any earlier US Airways operated flight that departs on the same day as your originally scheduled departure, you may change to that flight and we will automatically confirm your reservation for $50 for flights within the 48 contiguous United States and $50 for flights to Latin America, the Caribbean, Canada and Alaska. This lower confirmation fee replaces the usual $150 change fee, plus any differences between your old fare and new fare, for non-refundable tickets.
If there is not an open seat on an earlier flight that departs on the same day as your originally scheduled departure, you may stand by for that flight at no charge. Standing by at no charge is not permitted if we can confirm that there is an open seat available for that flight. Seats on completely booked flights may become available if passengers with confirmed reservations don't show up for the flight. Unlike a confirmed reservation, flying standby does not guarantee that you will get on the particular flight that you want and may involve waiting for two or more flights before a seat is available to you." See rules.