Warrenlm: in fact, I got 3 different kinds of vouchers because of flight delays and customer relation problems. No % off. Fine prints state that you can only use one voucher per ticket, which means that if your flights are regularly delayed, and UA gives you a $25 or $50 voucher each time, you have to buy as many tickets as vouchers, which is not fair (You don't have to spend money any time you want to use a compensation!!!!). So, it is UA representatives job to accept to combine several vouchers, that's why I had to phone and talk to an identified supervisor who decided on his own to accept the vouchers on one flight. To answer your question regarding terms, I am sure that I got a "service check" (can be an amount in $ or a mileage credit), and a "travel certificate". Not sure about the systemwide voucher. Each of them has different fare restrictions (W class or not, flights originating in the US or not, and so on...), this explains why UA employees have a lot of difficulties really knowing which vouchers can be accepted and combined. The best thing to do is to hold the phone and be patient until you get the answer you are waiting for....