The problem with traveller's Checks (heh, have to remember to use american spelling and not Canadian) is not that they are't cash. It's how long it seems to take people to fill them out.
For some reason, there is usually a line of people behind whoever has the traveller's checks and then the people behind them are forced to wait and guests seem to quickly get annoyed if it takes longer than a few minutes to check people in.
With a credit card # or a card, you just give the guest a form to sign, then you swipe the card and grab the keys for the guest and they can go. I can check a guest in in less than a minute if everything is correct and they leave very happy with a quick check in and a pleasant clerk.
I don't know why it is but it takes much longer with Traveller's Checks because they have to fill them out. When the guests start to figit behind the one with the Traveller's Checks during a check in, its taking too long and the others are getting annoyed.
I LOATH facing irate guests. It usually means they are rude to me and leave unhappy with their service (for some reason, guests get upset at the clerk even when the clerk did nothing wrong). A happy guest is a happy clerk.