I couldn't get Web support to do a multi-city itinerary.

Also, one odd ball scenario I ran into: online, you couldn't use it for less than the value of the voucher. I had a $250 voucher and was trying to redeem it for a flight. On the flight selection screen, it looked like it was $248 after discount. (The flight was labeled as having discount applied.) Going to the next screen, it showed that no discount was applied.

Web support was able to ticket it, but they clarified that you can't book online if it is for less than the value of the ecert.