I recently had very frustrating experience with US Airways. I traveled with them in June 2006. My flight was overbooked, and they asked for volunteer to give up their seats in return for a voucher. I gave up my seat, stayed in the airport for long extra hours, but later found out that I'm never able to use my voucher due to ridiculously limited seats/flights valid for voucher usage.
A number of facts:
First of all, during the five hours that I stayed at the airport waiting for the next departure flight after I gave up my original seat, three US Airways flights in a row were overbooked and asked for volunteers. This means they are probably intentionally overbooking their flights.
Second, this is my fifth time trying to make a reservation using my voucher but without success. Every time I tried to book more than one month in advance, and some of my traveling dates are just normal weekends, not to mention holidays such as July 4 or Christmas.
Third, they never told tell me that voucher usage is limited to flights/seats when they wanted me to give up my seat (they only say it will be valid in one year and domestic travel only). So I think I'm maliciously misinformed.
All in all, I think they intentionally overbook (three flights in a row!) and place ridiculous limitations on voucher usage so that they will never pay back the volunteers (five times, book one month in advance and didn't get a single one that fits my schedule!). Therefore, please don't be the fool like me traveling with them, or worse, give up your seat in exchange for a useless voucher (not to mention all the time I wasted on the phone with them trying to make a reservation)!